Computer Program

HARDWARE PROGRAMME
In computer we have the hard & software. The Hardware is the physical
components of a computer that can be seen, touched and handled e.g. Central
Processing Unit (C.P.U), Keyboard, Monitor e.t.c. Those that study or
practice hardware's are called technicians or engineers depending on the
level of training they acquired.

COMPUTER REPAIR, MAINTANCE, ASSEMBLING & CONSULTANCY
Hard ware's we have in computer are
1. Entire computer unit, which include;
a. CPU e. Monitors I. Scanner's
b. Cards f. Monitors J. Key Board's
c. Memory g. Ups k. Mouse
d. Circuit h. Printer L. Joy Stick
m. Speakers n. Digital Camera o. Webs Cam
p. Digital Pen


WE HAVE HARD WARE DEVICES:
1. Input Devices
2. Processing Devices
3. Output Devices
1. INPUT DEVICES: These are devices that are used to give commands to
the computer system they comprise of keyboard, mouse, joystick, scanner
digital, camera, web cam, etc.
A.KEY BOARD: This is connected to the system board through a cable of 4/5
pins; it runs through the circuits and through processor to the
motherboard. It is used to receive signal Input. Keystrokes are for signal
input, which are the numeric and alphabets.

TYPES OF KEYBOARD
1. Standard keyboard.
2. Enhance keyboard
3. Multimedia keyboard for internet
We have serial or Ps 2 keyboard


COMPONENT OF KEY BOARD
1. Casing
2. Key strokes
3. Magic processor board
4. Nursel/spring
5. Keypad
6. Cable connector


MOUSE AS AN INPUT DEVICE
A mouse is a pointing device. It is the most common type of input device
after the keyboard. A mouse has a ball which moves when the mouse moves.
Sensors detect this movement and this information is passed to the
computer, which translates the movement of the mouse to the movement of
the pointer on the screen. A mouse has buttons to activate this on the
screen. The left mouse button is often used as a shortcut to menus. Touch
pads and trackballs are other examples of pointing devices. It serves as
a support to the keyboard.


TYPES OF MOUSE


1. OPTO MECHINCAL: this type of mouse comes with mouse ball, vertical &
horizontal wheels.
2. OPTICAL MOUSE: this type of mouse is made up of micro board, which is
the optics (i.e. control wheel). Mouse may be communication port 1&2
for serial or comm. 1&2 for serial. Optical mouse always comes as PS2
or USB port
3. WIRELESS OR CORDLESS MOUSE: this mouse is optical in nature, it has no
wheel ball rather it has a remote attached to the mouse port and it
also works on limited distance. Cordless mouse are also USB port.
Universal serial port asset speed of a device.
CLASSIFICATION OF MOUSE ACCORDING TO DIFFERENT PORTS.
1. Serial mouse
2. P s 2 mouse
3. Multimedia mouse
4. usb mouse
5. wireless mouse
PARTS OF MOUSE
1. p-roller-vertical &horizontal
2. ball
3. buttons
4. mouse gurad
5. lens
6. magic processor board
7. casing


JOY STICK
Joystick is for game; it is also a game device. It is connected
through the game port.



SCANNER AS AN INPUT DEVICE
A scanner is a device that is used to input pictures and text into a
computer. They work by passing a beam of light of the image and sensors
collects information from
The reflected light .The data produced is an image, which can be changed
using special image editing software. If the image is a page of text, which
the user wants to be able to edit, then special optical character
recognition software must be used to convert the image of letters in text,
which can be edited using word processor.
TYPES OF SCANNER
1. Handheld Scanner
2. Flat Bed Scanner
1. THE HARDHELD SCANNER: This limited in size of scanning object except
you use merging method to merge your image or pictures. It will not be
effective.
2. THE FLAT BERD SCANNER: Is not limited in size and smaller areas of
scanning image. It has a high resolution. In scanning, the co lour
ranger can only be limited by the system's VGA Video graphic pray.
This means the newer the VGA the better the co lour.
DIGITAL CAMERA
Digital camera is an input device that is also used to capture image or
object through the chipset o the process or board on a focal receiver to
the memory that enable picture, images, objects to be capture and later
transfer to the computer as an input device. You need not to connect the
digital camera to the computer before snapping but after snapping you
connect then through image or object are copied into the hard.
WEBS CAMERA
WEBS means forum for an exchange of information. Web Camera is also used to
exchange ideas in the computer for this reason. It is called WEBS Camera
because of the Camera. It can be used in Chatting in the Internet and also
in live information or visual information.
PROCESSING DEVICE
Types of processing device we have are
1. MOTHER BOARD 11. HARD DISK DRIVE
2. CPU 12.
FLOPPY DISK DRIV E
3. MEMORY 13. RIBBON
4. CACHE 14. SCSI
5. VGA CARD 15. CD-ROM
DRIVE
6. SOUND CARD 16. POWER PACK
7. MODERN CARD 17. LAN CARD
8. TV CARD 18. CASEN
9. USB CARD 19.WIRELESS
CARD
10. ISDN CARD


MOTHER BOARD
Mother Board is one of the most important devices of the computer. It is
made up of chipsets and other logical devices or component. It is on the
motherboard that other cards derive their functions.
TWO TYPES OF MOTHER BOARD
1. OPEN BOARD – daughter cards are not intacted.
2. ON BOARD – daughter cards are intacted.
The open Boards use a lot of daughter cards and also has a detachable
processor while the onboard means that those devices that appear on open
board e.g. VGA, Sound, LAN, and Modern etc are right now logically built
into the board itself as chipsets.
On motherboard we have slots, which may be CPU slots for card or socket.
We have the PCI (Peripheral connection interface), which runs in 16 bits,
and 32 bits data transfer modem and the ISA (Industrial, Standard,
Architecture) it is longer than the PCI but works, in 8-16 bits optional.
AGP slots runs with cards of 32 to 64 bits on the motherboard you can
also find the memory bank. Some motherboards may have 2,3,4 banks. The
memory bank on the motherboard must be filled at least 2 out of 4 banks or
1 out of 2 banks for the system to be faster in running programs.

CENTRAL PROCESSING UNIT
This is the basic part of a computer that sends
Signals to the input and output devices. It is called the brain or the co-
ordinate. It consists of the following components
(1). Processor Unit (2). Memory Unit (3). Control Unit
(4). Arithmetic and Logical Unit.
PROCESSOR UNIT
It is a very small component that directs and controls the computer system,
it is the heartbeat
Of the computer system, it is also attached to the mother board..
TYPES OF CPU
We have two types of CPU namely;
1. Pin CPU
2. Pin less CPU
3. Socket CPU

PIN CPU-this are type of CPU that comes with pin on the processor on
itself.

PINLESS CPU- it doesn't deal with pin on the processor but has pin on the
socket (slot).
SOCKET CPU-this type of CPU deals with slots. It can be attached under the
board.
The CPU controls the Arithmetic, logical sequencing & front side (FSB)
Interaction with Cache. The CPU's sockets are made up of pins, which are
logically built to the core areas. Not every CPU socket will feat every
socket hence you must analyze your board for the type of CPU that will feat
in, so is applicable to CPU slots.
CPU speed is measured in mega hertz. MEGA stands, for million & HERTZ
Stand for Cycle for clock speed.
Many companies manufacture CPU e.g. IBM, INTEL, AMERICAN MEGATREND, AMD,
CYRIX ETC.
The cycle of a CPU determines the processing speed of the entire computer
units.
CPU ranges in Accordance with the manufactures like 8088 from Intel
80186, 80/286 (25-33 MHz) 80/386 (38-40 MHz) 80486, 80586, step by step


Pentium 1 with speed (70 –100MHZ)
Pentium 2 with speed (133-200MHZ)
Pentium 3 with speed (300-1000MHZ)
Pentium 4 with speed (1.2GHZ – 3.0GHZ, CORE 2 DUAL ETC)
Mega Hertz = MHz means Million
Gig Hertz = GHZ means Billions
Kilo Hertz = KHZ means Thousand
Because the CPU is to coordinate the activities of the system, it has
become important for the CPU manufacturers from time to time to upgrade
the stepping of the CPU to meet up with market demand especially in
software market. INTEL & AMD are the strongest, highest processor in the
market and contain some components on it for voltage regulation.
CAUTIONS FOR CPU
1. Make sure that the processor is the right one for the board.
2. Make sure that the processor has heat sink or fan on it.
3. Don't detach the CPU from the board while the system is still on; make
sure that you disconnect the power from the power pack exp, ATX board.


4. Check for proper jumpering for power of the CPU Core Voltage input and
output voltage.
5. Shut down the computer system properly; do not on or off the system
anyhow because you have to allow the fan on the CPU to stop.
A CPU can be upgraded but must be the same match for the slot or sockets.




PROBLEMS OF CPU.
System hanging.
System not powering.
Can power but not booting.

BATTERY: The type of battery used by the computer system is known as the
complementary metal oxide semi conductor (CMOS) battery, which regulates
the computer modular operating system. The Cmos battery takes care of the
setting of the board parameters e.g. the time and date of the computer
system. The type of battery that the motherboard carries is the Litton
battery with 3v capacity series CR 2002.When the Cmos battery is low or
spoilt, the Cmos configuration settings on the motherboard will be lost and
will need to be reset before the commencement of work for the day.
BIOS (BASIC INPUT OUPT SYSTEM)

Bios are a chipset that controls every input to the board and every output,
input to the board and every output that goes out of the board. Manually
every day before works commence, you will check it. Bios contain Rom
program
JUMPERS

Jumpers are meant to close or open a circuit connected to the device e.g.
hard disk drives, cd rom drives or Jumper 7 (located at the motherboard)
is for enabling and disabling the board parameters (i.e. restore default).
1&2 Clear Cmos (Disable)
2&3 users default (Enable)
After enabling or disabling a jumper, the settings need to be saved to the
cmos for the settings to be effective and for future use. You can also jump
your sound card, vga card, modem cards etc.
MEMORY
Memory in computing is the part of computer where information is stored;
the amount of space in a computer for storing information either
permanently or temporally.
TWO TYPES OF MEMORY
1. Permanent storage device(ROM)
2. Temporal Storage device (RAM)


Permanent Storage Device: This is a type of memory that is capable of
storing information permanently. E.g. of such devices are:

a. Hard disk
b. Cache
c. Rom (Read only Memory)
d. Magnetic Tapes, etc.
e.
HARD DISK
Hard disk is a permanent storage device. It is always tied to the
system i.e. why it is called fixed hard disk. The composition of the hard
disk includes the board, cylinders, the heads and sectors. The cylinders
are spherical in shape coated with magnetic substances from data.
* The Head is the starting point for every cylinder.
* The sectors are the division to which the cylinder could be divided. The
storage of the hard disk is measured in bytes. The older hard disk has low
capacity while the modern one has the higher capacities while the modern
one has the higher capacities files are permanently sacred in the hard
disk. Every hard disk from the factory is per-formatted. So for you to save
work, it must first of all be formatted in a higher level way. During
formatting, the operating system (OLS) will now prepare the hard disk into
cylinders, head and sectors. High processor board will carry a higher hard
disk while a low processor will carry a lower hard disk. If a higher hard
disk say 20GB connected to Pentium 1 series processor, it might have a draw
back because of a rotation per mint (RPM) compared to the processor clock
speed. So it is necessary to identify the processor of the system before
attaching to a system. Most hard disk gets crashed or bisector early
because of processor speed and unnecessary power failure or constant power
failure.
The company that manufactures hard disk includes, Sea Gate, Quantum,
Maxtor, fusion, International Business Machine (IBM) etc.
STRUCTURE OF THE HARD DISK


Track


Head






The read and write head starts from head & sector.
You can also know the capacity of your hard disk. By multiplying the
cylinder-Head and sector by size
JUMPER OF THE HARD DISK
A. Master indicates that the O/S will start the computer from the hard
disk. The master being the source does not depend on any other hard disk to
boot the system.
B. Slave hard disk cannot boot up the system to windows, hence to save or
copy information to and from the slave you must go through the master
first. Slave hard disk is used as a backup of the master hard disk.
C. Cable Select enables a system to select by itself in other words it
enable the system to automatically configure the hard disk jumper depending
on the boot of the system. Cable select may be necessary when you are
confused on the jumper of the system you will then the hampering of the
system you will then configure it as slave or master. Normally the pins for
jumper are eight (8) in number s

NOTE: Always follow the hard disk instruction for jumping.

HARD DISK HEAD CRASH
In a nutshell, a head crash is a physical damage of a hard disk when the
faulty electronics or mechanism causes the read –write head to land on the
rotating platter instead f retracting to its safe zone, hence by damaging
and grinding away the magnetic film on the disk surface.
A read-write head or simply the head is a tiny electromagnet suspended by
an armature that is prissily positional above every disk platter. The head
acts as an interface between the physical storage media and the rest of
electronics components of the disk by transforming electric signals into
magnetic pulses to store data into a disk in reverse, it reads the patterns
of magnetic flux and converts them into electrical signals which are
further encoded into binary bits to be processed by the computer.

How Does A Hard Disk Crash Happen?
When the platter is rotating at rates between 5,400 to 15,000 revolutions
per minutes, a thin film of air suspends the read/write head extremely
closely above the disk surface. The distance called the head is typically
measured in millions of inch. So it is possible that heads can make contact
with the media on the hard disk when they are faulty disk mechanism.

DUST DEBRIS.
A hard disk is never 100% seal if it is then, it is not possible to create
the necessary air flow from the disk working mechanism. When dust enters
and contactminated to the hard disk. It can obstruct the movement of the
head resulting in a crash as the clearances between the sizes of a smoke
particle.

MECHNICAL SHOCK
A sock applied to a disk while it's in active state may cause the head to
bounce and slide against the platter hence forth scratching it.

POWER SURGE.
Another reason is the effect of using poor power supply which has the same
problem as power surges and power cuts resulting in unpredictable movement
of read write head mechanism causing the crash.

WEAR AND TEAR.
Hard disk is complex and extremely delicate electromechanical devices that
subjects to wear and tear over time. They have a fairly predictable life
span even within a controller environment just like other mechanized
devices.

PROTECTION MEASURES AGAINST HDD CRASH.
With the advancement of technology platters manufactured today are guarded
with anti vibration technology to prevent the head from making contacts
with the rotating platter when a drive is shocked or jested. Protective
layers are also implemented on the magnetic surfaces of newer disks to with
stand a certain amount of head-crash abuse before permanent damage sets in
for instances, laptop computer hard disk are manufactured with better shock
resistance capability as these machines are typically on the moving.
However it is always recommended to avoid moving your computer while the
disk is still in operations.
CACHE MEMORY
Cache memory is the special type of buffer (G) memory that holds a copy of
data or instructions in main memory if they are likely to be needed by the
next processor. It generally increases the speed at which data and
instructions can be accessed and therefore the speed at which the task is
completed. Cache enhances software operation. A board with high cache of
says 256KB –512KB perform better than a board of 128 or 64KB.

READ ONLY MEMORY (ROM): This is a name giving to chips that store
information or instructions that do not change. An example would be the
instructions and data used when a computer is first turned on. The contents
of ROM memory are retained when the computer is turned off, therefore it is
non-volatile. The data or programmed stored in ROM cannot be altered only
read. Instructions that are stored in memory are called firmware or
macrocodes. Examples of computers that use ROM memory are the special-
purpose computers used in automobiles and appliances
MAGNETIC TAPE: this is a type of memory that is made with tape coated
magnetic material.
MAGNETIC DISK: This is the type of memory that is made with plastic coated
magnetic material

ALPHAPETICATION OF DRIVES
1. Floppy = A: 0r 3 1/2 floppy A:
2. Zip drive = B:
3. HDD = C:
4. CD ROM = D:
5. CD Writer =E: e.t.c.
Any of the drives that come into the system takes its own alphabet.



FLOPPY DISK
Floppy diskette is auxiliary storage devices because it is a temporal
storage device.
TYPES OF FLOPPY DISKETTE
1. 5 1/4 Floppy diskette
2. 3 1/2 floppy diskette
DS- Double density
HD-High density
The capacity for 3 1/2 diskette is (1.44mb, 2.88MB) the floppy
diskettes are made up of tracks and sector






FLOPPY DRIVE
Floppy drive is the device that accepts floppy diskette.


1)5 1/4 and 3 1/2 floppy drive is 360KB or 72OKB capacity of 3 1/2
floppy drives is 1.44MB, 2.88 MB of disk.
Each Floppy Disk Drive is Made Up
1. Read and Write head
2. Motor
3. Knob
4. Data Port
5. Power Port
6. Lever
7. Processor Control Board (PCB)
RIBBONS
Ribbons are used to connect a device to the motherboard. It is a
communication bridge between two components.E.g. Of Ribbon Connection Are?
1. From Hard Disk to the Motherboard
2. From the floppy to the motherboard
3. From CD Rom to hard disk or Motherboard
4. From VGA Ribbon to Motherboard
5. From mouse ribbon to motherboard.
6. Ribbon can also be used in other processor control board like
scanners, printers and monitors.
NOTE: That wrong polarity of ribbon connecting can cause device to
malfunction.
* The number one wire of the ribbon is always marked with Red or similar
colors. The wrong connection of ribbon can make a system not to detect the
hard disk or could cause the cd-rom to malfunction by refusing to eject the
cd-rom when the button is pressed floppy every motherboard you buy must
come with its ribbon.

CD ROM DRIVES
CD –ROM drive is an advancement in storage technology just as floppy drive
in and auxiliary storage Device so also is the CD ROM but in a higher
density. A typical CD –ROM Drive has a capacity for 650 MB to 800Mb Rom
(Plates)
CD = Compaq disk /Rom (read only Memory)
A CD-ROM Drive Comprise of
1. Lens 7. Ribbon & Connector
2. Motor 8. Speaker in & out Audio Connector
3. PCB 9. Jumper for Drive (MS,SL, CS)
4. Puller
5. Knob for eject


The CD Rom drive is measured in rotating per minute rated as X eg. 4X,
8X, 12X, 16X, 24X, 32X, 38X, 42X, 46X, 52X, 56X,
TYPES OF CD –ROM DRIVES
1. CD ROM DRIVE
2. CD /DVD DRIVE
3. CD REWRITABLE DRIVE
4. CD-DVD –COMBO DRIVE
FORMATING A NEW HARD DISK
Formatting is the division of the hard disk into tracks & sectors.

1. Temporal Storage Device: This is where data or jobs are kept temporary
inside the computer system before processing; this means if there is a
power failure while working, all the information or data on the
temporal memory will be lost. Examples of such devices are:
RANDOM ACCESS MEMORY (RAM):
Ram is the name giving to integrated circuits, or chips that are used for
main memory. It is temporary memory that allows you to run applications.
When a computer is turned off, data stored in ram memory are erased,
therefore RAM memory is volatile. Programs that need to be saved need
to be transferred to the secondary memory before the power is turned off. A
new type of memory called flash ram or flash memory can now retain data
even when the power is turned off. Many applications require specific
amount of ram to work, fortunately, more memory can be added. Examples of
temporal device are: -
a. RAM (Random access Memory)
b. SIMM (Single Inline Memory Modules)
c. DIMM (Direct inline Memory Modules)
d. DRAM (Single Data Random Access Memory)
e. DDRAM (Double Data Random access Memory)
SIMM Comes in 30, 32, 72 pins for 386 or 486 boards
DIMM Use 84 pins and above.
All Memory are measured in bytes, bytes stands for characters then 8 bits =
1 byte = 1 character
A bit is the smallest identifiable unit in information storage or Data
storage.
Memory works for program whereas processor works for the Board. The higher
the memory in your system the faster the programs in your system.

MEASUREMENT OF MEMORY
Memory can be measured in: -Memory is measured in bytes, which can also be
measured in binary numbers.

HOW TO KNOW THE CAPACITY OF MEMORY
1. It can be known through a paper pasted on the memory indicating the
size of the memory.
2. It can also be dictated when you insert the memory on the board, while
the system boots it will show the capacity of the memory.
3. It can also be known through this way, click on start, click on
control panel, and double click on system.
CAUTIONS FOR THE MEMORY
1. Bring out the memory and use mentholated spirit to clean the pin,
capacity Bios etc. keep for about 2 hrs dry or day to dry. But before you
insert it back, blow off the dust in the banks before inserting the memory
again to avoid affecting it again.
DIAGRAM OF A MEMORY








HOW TO KNOW WHEN MEMORY IS BAD
1. It cannot boot the system
2. It will not give normal count (e.g. 256mb of ram gives 64mb)
3. The memory will beep for 3 times
4. A bad memory cannot load any O/S or program e.g. when system hangs or
give error massage you know that the memory is bad.
For a program to run especially operating system, system must meet the
memory requirement for windows e.g.
Win 3.1 requires from 2mb and above
Win 95 requires from 4 MB ad above
Win 97 & 98 requires from 8mb and above
Win ME may requires from 32mb and above
Win 2000 may requires from 64mb and above
Win XP may requires from 64mb and above
NOTE: It is better to have higher memory for application programs to run
effectively.
HOW TO PURCHASE MEMORY
SIMM = 1mb –8mb
DIMM = 8mb – 32mb
S DRAM =32-64 –128-256 -512
DDR = 64 – 128-256 512mb RAM.
MEMORY SLOTS
EDO RAM memory slot
Sdimms Memory slot
DDR Memory Slot
Dimms Memory Slot
The speed of a memory is measuring in nano second and it volume is in
bytes.
CAUTION
Do not try to mismatch memory


VGA CARD
Video Graphical Array or Adapter can be onboard or can be an Adaptor a
card. VGA enhances the display of the screen in other words; it is the
bridge between the CPU and the monitor. VGA Card comes in variety; it can
be ISA, PCI or AGP Advantages of onboard VGA depends on the onboard memory.

DEMERITS OF VGA` CARDS
1. It will refuse to display on the monitor
2. It will give a beeping sound via the buffer
3. It will boot and the screen will be blank half way.

SCSI CARD
SCSI means small computer system interface. It is a system card designed
to spring up process device.
SCSI card, which acts as add –on –card for the board. The configuration of
pins in the SCSI Card is quite different from the conventional cards. Most
boards come with IDE or SCSI cards.

SOUND CARD
Sound Audio processing card is used to capture chipsets and then processes
the audio in form of sound transmission, it travels in Hertz
HOW TO INSERT SOUND CARD
It can be onboard or adapter. In any well-installed sound card, you must
have the mic connection port, the speaker ports and in and out ports also.
INSERTING METHOD.
1. Insert the card to the system slot whether ISA or PCI Slot
2. The system will detect the card as a new hardware
3. Insert the driver that it comes with weather CD driver or a diskette
4. The O/S will automatically search for the inserted driver to install
the software then click next until it installs the software.
5. If properly installed the Audio will function else it will not
function.

MODERM CARD
Modem means Modular Demoduler that has to do with analog digital card; this
is a device that is used in converting telephone language to computer
language from Nitel in Nigeria to public phone of data in computer world.
TWO TYPES OF MODERM
1. INTERNAL & EXTERNAL MODERN: Digital is faster than Analog. Digital goes
straight while Analog goes rigorously Analog Digital.
Dates always are in Bits this modern have a data rating
In kilobytes.
The line is bought through the Nitel line to the back of the modern
card. The cable that comes at the back of modern card is called BJU. Modern
is for telephone dial-up and Internet connectivity. To install a modern
card the modern must have its driver.
RANGE OF MODERN
It ranges from 32.6K BPS or 56BPS KBPS (Kilobytes per second)
INSTALLING A MODERN CARD
1. Uncouple the system and insert the modern card in a slot at the mother
board
2. Reboot the system
3. New hardware found massage will appear on the screen
4. Then insert the CD driver that it comes with.
5. The O/S will ask you whether you want to install automatically or
manually
6. The system will install the driver and make it ready for use.
PROBLEM ASSOICATED WITH MODERM
1. Modems are open or prone to dangers during lightning
2. Moderns are likely to short circuit if not properly handled
3. Modern will not connect if other country codes are used instead of the
user country
4. Power upsurge can damage the modern


LAN CARD
Local area network card can also be called Network interface card (NIC)
Network card (NC)
LAN Card is used as a physical device in Networking; cables are connected
through the computer and Network card. Most Network cards runs on 10 by
100 BPS, which stands for million bytes per second on 100 meter, range
MBPS
RX receiving and Exchange
TX transfer and Exchange
TYPES OF LAN CARD
1. PCL LAN CARD
2. ISA LAN CARD
3. WIRELESS LAN CARD

TV CARD
TV card is an integrated Card that enables the system monitors to be used
as a channel or means to connect you to TV channels. A VGA Card can also
have TV cards on it. You card install the software and then use your
monitor as TV.

U S B CARD
Universal serial Bus/Board is a device that enhances the new technology
system. It is a plug & play device (PNP). It can be inform of a card or a
cable. The USB card or cable works faster than any other conditional card
or cables i.e. 2.X speed of other related devices. It is universal in
nature that is why it be used for mouse, printer, keyboard, scanner.etc
A typical USB Card must have a driver, some new technology system and
devices comes only with USB port.
USB Cable or card carries an option in or out during processing. Old
model motherboard e.g. does not have the onboard USB facility. Hence to
connect a USB device you must purchase a USB Card to install.
* Multi 10 Card is an old ISA Card formally used for 386, 286 formally used
to connect hard disk, floppy, mouse. It was useful then because those mouse
286, 386 has no on board mouse, hard disk, and floppy connector. Every card
must be inserted on the PCI or ISA Slot.

ISDN CARD
Integrated service for Direct Network (ISDN). It is a dial up Internet
telephone service that can be used for voice and data. Hence to connect to
the Network of this service, you must have an ISDN card in your computer.
The card can be Internal or external, most of the external ones use
USB Configuration. It is different from modem in the sense that it is
regarded as a Network device. The providers of such services in Nigeria are
the Nigerian Telecommunications Ltd (NITEL). NITEL is able to provide such
service because they are apex or gateway of communication.
* The ISAN card runs on a higher board rate more than ordinary modem. The
slowest speed for a typical ISDN Card is 64KBPS. The card must be installed
with the driver that came with it. After the installation, you configure
the Card for Internet.
* The Internet ISDN card comes as a PCI card the highest speed of a ISDN
card is 128KBPS.


POWER PACK
Power Pack is a device that connects power from DC or AC power outlet
devices to enable them function electronically. Power pack can be a
distribution point for MONITOR, system Printer, Scanners, and every other
device that uses current. It is made up of the primary & secondary unit.
The primary side/part is an input side while the secondary part is the
output side.
TWO TYPES OF POWER PACK
1. At power pack is manual in power relay (Advanced Technology)
2. ATX power pack is Automatic in power relay (Advanced Technology
Extended)
ATX power pack act with the operating system on Display power management
system (DPMS) but AT Does not have such facilities. Diodes connect power
from AC to DC.
ATX has about 20 pins with colored cables. In ATX the fellow wire carries
more voltage that others + or – 5v. The more power that goes to the board +
or – 12v or + or – 15v you will be careful while slotting the ATX pack to
the board and do not change polarity.

PROBLEMS ASSOCIATED WITH POWER PACKS
1. When the power pack is subjected to high voltage than the fuse and
capacities, resistors etc cannot contain, it will blow up such
components
2. Wrong polarity
3. Dust Accumulation in power packs will cause bridge to power pack hence
you should make your computer is dust free
4. Inappropriate connections of ribbons cables can also cause the power
pack to malfunction.
SOLUTIONS
1. Change some components that are bad
2. Troubleshoot the power pack, which mean checking for component, which
are bad and change them.


ASSEMBLING CARDS
In a system where you have LAN, modern VGA, US6 and sound card you can
put VGA in I or in 3 or VGA in I, modern in 3. If you did not insert the
right card 60 its sitting, there will be conflicting. Try to insert your
cards in a slot.
During the process of assembling the system you should be careful on
how arrange the cards in such that they can properly adapt non-
conflicting IRQ the cards.
Dual forts in first out (FIFO)
Last forts in first out (LIFO)


COMPUTER ASSEMBLING
It is the process of identifying components that have common connecting
function and joining them to achieve particular objectives. It is also a
process of rejoining devices as anointing.
Before assembling a system you must be Familiar with the system a
components as wrong connection of component to component will result
acute malfunction.
ITEMS FOR COMPUTER ASSEMBLING
1. CASEN which might be AT or ATX, Tower or flat type of case
NOTE: the type of motherboard you buyer determines the type of case
you buy. We have:
1. AT CASEN
2. ATX CASEN
New Casein you buy must have:
1. Power Pack
2. Power cable
3. Screws
4. Extra brackets
After assembling a system test it before you couple the system. Which
means are you couple the system. Which means after testing outside
disconnect and stage of your assembling you must test before slotting
ribbons.
ASSEMBLING
INDICATORS ON MOTHERBOARD
TYPES OF INDICATORS ARE
1. Power Indication (Port)
2. Hard disk Indicator (HDD)
3. Power Switch (person)
4. Speaker (SPK)
5. Reset (RST)
6. Turbo (Turbo)
In AT mother Board power indicator you don't power through the board
but through the knob because you have a direct power through the knob.


As IN ATX the power through the board
POLARITY FOR CABERS
Black (BI) –Ve
Brown (BR) + Ve
Red (R) –Ve
White (N) + Ve
NB: you should know that connecting of indicators helps the engineer
to
1. Trouble shoot the computer
2. Operator to understand the working aspect of the system such as
when the hard disk light is blinding, power the hard disk light
is blinking, power on etc.
After Assembling and it tests step is installing of OLS.

OPERATING SYSTEM (OS)
It is a program that acts as an inter face (Go between) for the user and
the system. The level of language you see on the screens called the high
level language and then converted to low languages or machine language so
that the system will understand.
The O/S also acts as an interpreter between the user and the machine
because the machine will not understand the high level language but before
the computer understands it must be decoded or converted to machine
language.
THE OS IS DIVIDED INTO TWO.
1. Non graphics os.
2. Graphics os
EXAMPLES OF NON GRAPHICS OS.
1. Windows
2. Network
3. wireless
EXAMPLES OF GRAPHICS OS
1. Mac
2. Linux
3. Zen ox
4. Unix

HOW TO INSTALL OPERATING SYSTEM
Thing to do before installing O/S
1. Partition the hard disk before formatting or you go on to formatting
hard disk before installing the operating system.
2. If it has an already version of O/S you can up Grade the operating
system
HOW TO PARTITION A HARD DISK
1. Formatting (dividing the hard disk into tracks and sectors)
2. Verifying
3. Checking clusters
You can have full partitioning meaning to use the whole of the hard disk
Diver partitioning (part by bard) you can partition the hard disk when the
HDD is old and may have some problems.

FORMARTTING
Formatting is the process of preparing the HDD to receive data. Data cannot
stay in the HDD because during the formatting process the hard disk
cylinder will divide into tracks and sectors
NOTE: BEFORE FORMATTING A COMPUTER YOU MUST SET YOUR BIOS, SOME KEYS USED
TO ENTER SETUP, F12, F2, AND DEL.
Now the computer will ask you press any key to boot from cd/DVD, press the
key without wasting time
(DOS) DISK OPERATING SYSTEM
Dos are the priest operating system that started the method of booking
computer from the permanent Medium. MS DOS as it is called is the most
popular on in the market. Dos itself is a command interpreter.
INTERNAL COMMANDS
These are those commands that are visible in the dos directory
EXTERNAL COMMAND
These are those commands that are not visible in Dos Directory but if you
issue such commands it works.
Examples of Internal Command are:
C:/Dos Dir
Command. (Com) – Extension
Copy. Exe * Backup
Print. Exe ANSI Restore
Delete
Rename
Auto exe
Tree
Deltree
X copy 32
Edit
EXTERNAL COMMAND
US – Clear Screen
Dir – directory
Wild card - *
MD – make directory
RD – Remove
CD – Change
/ - Root
CD. – Step out to root
: - File extension
CD * - step out

Assignment
1. Formulate a technical command that will help you to change from one
drove to another
2. Give two examples of internal command you can use a technician during
repairs
: ANSWERS:
1. C: / A; C: / D: ; C: / E: etc A:/ C
12. X copy command & deltree command
HMA (High Memory Area)
ANSCII: American Standard Code for Information
1a From C: Prompt you want to change to floppy you under C: prompt C: / A:
B. if you are In A: prompt & want to change to C: you types A:/ C:
SOLUTIONS
Drives: A: B, C: D; E; F; 2
Then to change from one drive to another, from the current drive eg C: the
next drive e.g. A: type C: / A:
This is how to change from one drive to another. Autoexec is a batch files
that written by the system user. Auto exe bat file is for program
everywhere you see if it means flagging
2. Restore: this is used to restore your old setting on the computer. C: /Y
Scanner restore
b Scanning (Scan registry) it can be used to scan registry & there will
restore take
c. Scan Disk: this is used to scan the total disk area for error if the
computer sees any error and ask you did you want to fix it just priest
enter for fix it the problems C:/ Scan disk
d. CHK DSK: - this is used to check disk space etc C:/ CHDSK/F
X Copy 32 is used for cloning or is used in making a duplicate of a hard
disk. To use this command, there music is a two hard disk available at that
moment. The first HDD will be the source while the second HDD will be the
TARGET or Dest nation.
The source is the primary master that one is the Functional one the
Destination is the primary slave which is the empty HDD of which will be
formatted, then you enslave it to primary slave.
Source = primary Master
Destination = primary slave
HOW TO ISSUE X COPY 32 COMMANDS
From C: prompt type
C: / x copy 32 C: /D: e\h\r\v press
This command works better in window 95, 97, and 98 & wins me. After cloning
remember to rejumper the slave into master.
COMMANDS
1. Auto exce bat: this is used to write software or programs
2. config. Sys this for devices
3. Deltree is used to delete tree
4. C:\this is the root
5. – Prompt.
HOW TO DEL. TREE
1. Type C: \ Deltree C: \ window
HOW TO DEL TREE IN A:
1. Type A:\ Deltree C:\window
This command will delete any thing called window but it wil save some of
the files but as in C: prompt it with automatically deletes everything.
You can also just delete commands inside window and leave window alone
whether in C: or a:
Command. Com:- this is a file that controls the booting up of your system,
without command . Com file your computer will always be reporting missing
operating system which means the operating system cannot work with out the
command. Com
* Some of the hidden command in the system is hidden for it to be delected
SOME HIDDEN COMMAND ARE
* Command. Com
* System .com this is used to transfer to the medium command
* I.O.System
The character you will see when you edit command .com is ASCII.
If you came across A:\ when you are booting with your diskette or CD know
that you are booting your system with a bootable CD or Diskette
After booting with your bootable under A:\ type A:\ system –C: it will
copy command. Com to your hard disk
ADVANTAGE OF COMMAND. COM
1. It helps to upgrade a system
2. It helps to repair software problem
3. It helps you to have access to your system.
BACKUP COMMAND
Backup is a process of preparing or preserves a or group of files as
backup files or directory in another medium a part from the source that
is the main file. This files or directory that are reserved in another
medium a part from the source acts like a copy of the source eg back up
001,002 according to the number of backup made
NB. An entire HDD or diskette may be backed up. In Dos prompt
backup command is very prominent.
How to issue backup command
C:/ back up –A: A:
C: C:
Source Destination
Every backup must be accompanied with restore command with immediate effect
DEFRAGMENTATION
Defragmentation is the arrangement of files in an order manner. It show be
done at least every 2 or 3 weeks of work on your computer.
COMMANDS
Attribute (Attrib)
Rename (Ren)
* Attribute is an notation used for setting file characteristics.
The parameter for attribute is +
+ Means Hides
- Means release
h means hidden file while
r means read only
ASSIGMENT
How do you reverse C: attrib + h + r \ my document \ Ernest document there
is an access denied while trying to delete Ernest. Document after word.
RENAME
Rename is an internal command. The shortcut for rename is (ren). Rename is
used to change a file name in to another name or the reason while you
want to rename the file is because you don't want anybody to have access to
that file or folder under C:\ type C:\ ren -\ my document 1-\ NetWare cdr -
\ job. Cdr
: ANSWER:
You have to enable Ernest document before you can delete it
1. C:\ attrib – h-r \my document \Ernest document
2. Deleting ernest execute file
WINDOWS OPERATING SYSTEM (WOS)
Window operating system is an enhancement of disk operating system. It is
called a graphical user interface (GUI). The OLS is developing to be user
friendly, flexible, tasking program.
Window program are made up of Icon or items some Icons can be animated.
Items here represent the program installed and Icons represent other basic
program e.g. coral draw, page maker etc
ASSIGMENT
1. 6 Basic differces between dos & Windows and Explain
ANSWER
1. Windows have flexible, mult tasking environment, but Dos does not have
such environment
2. Windows programs are made up of Icons which can be animated but Dos
programs has (None)
3. In Windows it require mush HDD space but Dos requires a little
4. Windows supports/Networking but Dos programs does not support
Networking
5. In Windows operating system must be installed operating system must be
installed before installing program but in Dos it has its own based
programs which deals with command
6. In Windows Icons represent something but dos has no Icons
NB. It is easy to give command in windows than in Dos because of mouse
clicking.
In every OLS they must be a corresponding program to run in when for e.g.
programs written.

WE HAVE TWO CLASSES OF PROGRAM
1. Soft ware or system software
2. Application program
System programmes are those programmes that acts as an interface between
the user and the computer called OLS. Other system which are read only
memory programmes which are coded into Bios, Caches processors & Co-
processor etc. most of the programmes that run from the clip sets from the
factory board are the P Rom and EP Rom
P Rom stands for programmable read only memory while EP Rom stands
for enhanced or electronics programmable read only memory.
Application programmes are the programmes that programmers can
write for day-to-day running eg Graphic packages, games, accounting package
etc.
PROCEDURED OF INSTALLING OLS
Windows operating system like other operating system comes in diskette or
in CDS. The earlier versions of which WS eg. 3.0, 3.1, 3.11 comes in
diskette but because of the latest vulnerability to damage, the latest
versions of win. Comes in CDS eg Win 95-97, 98 etc to install windows,
there are two methods
1. Clean installation & (2) upgrade
CLEAN INSTALLATION (PROCEDURES)
To do a clean installation, you must have:
1. Hard disk (formatted)
2. Bootable Windows CD
3. Enough Memory to run windows
4. Enough or good CD –Rom or diskette drive for installation.
Before formatting a hard disk check the space available whether it can
be able to carry the windows you are about to install.
1. Win 98 requires 2 GB HDD space
2. Win me & 2000 requires 3GB HDD space
3. Win XP requires 4GB HDD Space and upwards
MEMORY CLASSIFICATION FOR WINS
1. Win 9s & 98 requires 8MB Ram or higher memory to run effectively
2. Win me requires 16-32 MB Ram
3. Win 2000 – requires 32 MB Ram
4. Win XP – Requires 64 MB ram upward
After formatting the hard disk code OLS.
CLEAN INSTALLATION PROPER
In win 98 their CDSA that is the original, which came with a new PC this,
can be used automatically to format a new hard disk. Proceed with the
installation of win proper but if you decide to quit setup after formatting
the hard disk press F3 twice to exit setup and to return to prompt and
setup the version of Ols you needed.
In the areas of win 2000, xp, just insert the installation CD
containing the Ols into the CD-rom drive and restart the system. As the
system is booting enter the board level to change the command to boot from
CD-rom after changing press F10 and to exit. The CD of
this window runs Auto play, and then follows the installation procedure to
install this ols.
In Win 98 it has a cap file but in Win xp and 2000 it has no cap
files in win 95-08 installation are done manually but as win xp and 2000 it
is done Automatically.

UPGRADING OLS
NB: before you can upgrade an ols it means that the Ols will meet the
minimum requirement of the upgrade eg upgrade win 95 to win 98, 98-2000, me
or xp.
TO UPGRADE WIN 95
:REQUIREMENTS:
1. The window will be running in the system
2. memory must be greater than 8mb or more than
3. Hard disk space must be greater than 400mb so is the same with win 98.


All this conditions are needed because the system files of the old
version of win. You upgrade will be saved if needed that is there is
still room to uninstall the new version in future if need be.
REASONS WHY WE UPGRADE
1. Taste: reason blc he wants to belong to the current Ols.
2. Because of the application programmes he or she is running
3. Because of devices
4. Because of operating environment eg Networking, internet
5. For High productivity and efficiency
HOW TO UPGRADE
1. Insert the upgrade version of window CD into the CD rom drive after
the precious win you want to upgrade has finished booting normally.
2. The Ols CD will prompt for an upgrade or clean installation you set
upgrade
3. Follow the instructions on the screen
4. You can upgrade from win 3.0 to 95,97 or 98 from 97 and 98 to me,
2000 or xp. Apart from upgrade system or ols you can also upgrade
devices.
ASSIGMENT
1. Give three examples of device that can be upgrade before installing
Ols
2. What is the different between system after and application files
3. Give five reasons why computer users upgrade their system
4. What can hinder upgrade of Ols
5. A system hangs while upgrading what the problem?
ANSWERS
1a. Memory can be upgraded
b Hard disk can be upgraded
c. Processors can be upgraded
2a. System files are that make up the operating system eg Win 98 se,
upgrade etc.
b Application files are files that are install after the installation Ols
that is system files eg Corel Draw, page maker etc.
3a the user wants fast and efficient system which can run H/Her program
fast
b. This is because of the types of devices He or she has like memory VGA
etc.
d. Thrist to upgrade the vision of Ols
e. The type of Application program He/She is running.
4. Memory hinder upgrade because if the memory in your system is low eg
like 16mb it cannot run win 2000 or xp.
a. Memory hinder upgrade because if the memory in your system is low eg
like 16mb it cannot run win 2000 or xp.
b. HDD space can hinder upgrade because if you have a little disk space
it cannot capacitate a upgradeable ols.
5. Bad memory can hang a system while upgrade. Just replace with a good
THINGS THAT HANG COMPUTER WHILE INSTALLATION OF WINDOWS
1. Bad and unreliable memory
2. Hard disk may have bad tracks or sectors
3. Conflicting cards or devices ie IRQ
4. Bad CD rom or CD rom drives
5. Bad Cache expecially external caches
SOLUTION OR PROBLEM WHILE INSTALLATING WINDOWS
1. As for bad memory, remove the bad memory and replace with a good one
and you can blow out dust from the memory banks with your blower
before inserting the good memory. You can as well clean the bad memory
with mentholated spirit and leave to dry. If it continued to hang the
system replace with another good one.
2. As for bad tracks and sectors,
A Use low level format to delete the bad tracks
B Partition the hard disk to good sections
C Limit your installation to Ols to the partitioned space blc it can take
all the space and none will be left for application programs
D After all this and it continues to hang the system change the hard disk
CONFLICTING CARD OR DEVICE
Solution checks out for the conflicting card and places them in their
right position.
4. BAD CD ROM DRIVE OR PLATE
Solution as for the Disk or plate if it has cracks all over and it hangs
the system remove and replace with good one. As for CD Rom Drive, open
the drive and clean the lens with spirit leave for some minute, then
cover and try again if it persist replace with good one.
5. Solution To Bad Cache
Solutions go to the board level and disable the external cache because
win. Will always check for external cache during installation.

FORMATTING OF FLASH OR HARD DRIVE USING
DISK OPERATING SYSTEM (DOS).
1. Run-cmd
2. Cd/ enter
3. Cls enter
4. Format space (e:) depending were the drive lies.
5. Press enter when ready –enter
6. Volume label-means if you want to name the drive
7. It will display some note telling you that your drive has been
formatted
8. Type EXIT-enter


SOME COMPONENTS FOUND IN THE MOTHERBOARD BOTH ACTIVE AND PASSIVE
COMPONENTS.
ACTIVE COMPONENT. These are component which have the ability to produces
gain.
Transistor
FET
Jfet
Mosfet
Diode
PASSIVE COMPONENT. These are component which do not have ability to
produces gain.
Resistor
Capacitor
Inductor
IC INTERGRETED CIRCULT

IC-INTERGRETED CIRCULT. It is a completely electronics cct in which active
and passive component are fabricated on a tiny single chips of silicon.





IC TERMINOLOGY.
BONDING-attaching the die on the ceramic substrate and then connecting the
leads to the package.
CHIPS-an extremely small part of a silicon wafer on which ic is fabricated.
CIRCULT PROBING-testing the electrical performance of each ic chips with
the help of a microscope and multi-point probe.
DIE-same as chips.
DIFFUSION-a process that consist of the introduction of in purities into
the selected region of a wafer to form junction.
ENCAPSULATION-putting a cap over the ic and sealing it in an inert
atmosphere.
EPITARY-a process of the controlled growth of a crystalline doped layer of
silicon on a single crystal substrate.
ETACHING-a process of selective removal of a region of a semi conductor
metal or silicon dioxide.
MASK-a glass plate with desired pattern for diffusion or metallization.
METALLIZATION- a process for pro viding ohmic contacts and
interconnections by evaporating aluminum over the chips.
PHOTOLITHOGRAPHY-a process to transfer geometrical pattern from the mask to
the surface of the wafer.
PHOTORESIST-a light sensitive material that hardens when exposed to
ultraviolet light.
WAFER-a thin disk of semi-conductor in which number of ics are fabricated
simultaneously.



Testing an Integrated Circuit Wafer
In its final stage of design, an integrated circuit wafer is tested by
probes. Each gold square in the wafer is an individual integrated circuit.
At one time, circuits consisted of separate electronic devices (such as
inductors and capacitors) mounted on a chassis and strung together with
wire. These circuits were easy to manipulate by hand, but they were
extremely bulky. In contrast, integrated circuits incorporate all of the
separate electronic components on a single board.

HOW ICS ARE MADE
The ics are manufactured in four district stage namely.
1. material preparation
2. crystal growing and wafer preparation
3. Wafer fabrication and testing, bonding and packaging.
4.
THE DEVELOPMENT OF IC
Beginning in the late 20th century, integrated circuits based on
silicon chips shrank rapidly in price and size while expanding in capacity.
These advances in chip technology contributed to a boom in the computer
industry. The creation of a single silicon chip requires hundreds of
manufacturing steps. In this Scientific American article, Intel Corporation
president and chief operating officer Craig R. Barrett describes the chip
manufacturing process from design through completion.
From Sand to Silicon: Manufacturing an Integrated Circuit
The fundamental device of the digital world is the integrated circuit, a
small square of silicon containing millions of transistors. It is probably
the most complex of man-made products. Although it looks flat, it is in
fact a three-dimensional structure made by painstakingly building up on the
silicon base several microscopically thin layers of materials that both
insulate and conduct electricity. Assembled according to a pattern
carefully worked out in advance, these layers form the transistors, which
function as switches controlling the flow of electricity through the
circuit, which is also known as a chip. 'On' and 'off' switches manipulate
the binary code that is at the core of what a computer does.
Building a chip typically requires several hundred manufacturing steps that
take weeks to complete. Each step must be executed perfectly if the chip is
to work. The conditions are demanding. For example, because a speck of dust
can ruin a chip, the manufacturing has to be done in a 'clean room'
containing less than one submicron particle of dust per cubic foot of air
(in contrast, the average living room has between 100,000 and one million
particles per cubic foot of air). Much of the equipment needed for making
chips embodies the highest of high technology, with the result that chip
factories—which cost between $1 billion and $2 billion for a state-of-the-
art facility—are among the costliest of manufacturing plants.
A basic technology of chips making is the 'planar' process devised in 1957
by Jean Hoerni of Fairchild Semiconductor. It provided a means of creating
a layered structure on the silicon base of a chip. This technology was
pivotal in Robert N. Noyce's development of the integrated circuit in 1958.
(Noyce later became co-founder with Gordon E. Moore of Intel Corporation,
the company that invented the microprocessor and has become the world's
leading supplier of semiconductor chips.…) Bridging the gap between the
transistor and the integrated circuit, the planar technology opened the way
to the manufacturing process that now produces chips. The hundreds of
individual steps in that process can be grouped into a few basic
operations.
Chip Design
The first operation is the design of the chip. When tens of millions of
transistors are to be built on a square of silicon about the size of a
child's fingernail, the placing and interconnections of the transistors
must be meticulously worked out. Each transistor must be designed for its
intended function, and groups of transistors are combined to create circuit
elements such as inverters, adders and decoders. The designer must also
take into account the intended purpose of the chip. A processor chip
carries out instructions in a computer, and a memory chip stores data. The
two types of chips differ somewhat in structure. Because of the complexity
of today's chips, the design work is done by computer, although engineers
often print out an enlarged diagram of a chip's structure to examine it in
detail.
The Silicon Crystal
The base material for building an integrated circuit is a silicon crystal.
Silicon, the most abundant element on the earth except for oxygen, is the
principal ingredient of beach sand. Silicon is a natural semiconductor,
which means that it can be altered to be either an insulator or a
conductor. Insulators, such as glass, block the passage of electricity;
conductors, such as copper, let electricity pass through. To make a silicon
crystal, raw silicon obtained from quartz rock is treated with chemicals
that remove contaminants until what remains is almost 100 percent silicon.
This purified silicon is melted and then formed into cylindrical single
crystals called ingots. The ingots are sliced into wafers about 0.725
millimeter (0.03 inch) thick. In a step called planarization they are
polished with a slurry until they have a flawless, mirror-smooth surface.
At present, most of the wafers are 200 millimeters (eight inches) in
diameter, but the industry is moving toward achieving a standard diameter
of 300 millimeters (12 inches) by 1999. Because a single wafer yields
hundreds of chips, bigger wafers mean that more chips can be made at one
time, holding down the cost per chip.
The First Layers
With the wafer prepared, the process of building the chip's circuitry
begins. Making the transistors and their interconnections entails several
different basic steps that are repeated many times. The most complex chips
made today consist of 20 or more layers and may require several hundred
separate processing steps to build them up one by one.
The first layer is silicon dioxide, which does not conduct electricity and
therefore serves as an insulator. It is created by putting the wafers into
a diffusion furnace —essentially an oven at high temperature where a thin
layer of oxide is grown on the wafer surface.
Removed from the furnace, the wafer is now ready for its first patterning,
or photolithographic, step. A coating of a fairly viscous polymeric liquid
called photoresist, which becomes soluble when it is exposed to ultraviolet
light, is applied to the surface. A spigot deposits a precise amount of
photoresist on the wafer surface. Then the wafer is spun so that
centrifugal force spreads the liquid over the surface at an even thickness.
This operation takes place on every layer that is modified by a
photolithographic procedure called masking, described in the next step.
Masking
A mask is the device through which ultraviolet light shines to define the
circuit pattern on each layer of a chip. Because the pattern is intricate
and must be positioned precisely on the chip, the arrangement of opaque and
transparent spaces on a mask must be done carefully during a chip's design
stage.
The mask image is transferred to the wafer using a computer-controlled
machine known as a stepper. It has a sophisticated lens system to reduce
the pattern on the mask to the microscopic dimensions of the chip's
circuitry, requiring resolution as small as 0.25 micron. The wafer is held
in place on a positioning table below the lens system. Ultraviolet light
from an arc lamp or a laser shines through the clear spaces of the mask's
intricate pattern onto the photoresist layer of a single chip. The stepper
table then moves the wafer the precise distance required to position
another chip under the light. On each chip, the parts of the photoresist
layer that were struck by the light become soluble and can be developed,
much like photographic film, using organic solvents. Once the photoresist
is patterned, the wafer is ready for etching.
Etching
During this step, photoresist remaining on the surface protects parts of
the underlying layer from being removed by the acids or reactive gases used
to etch the pattern on the surface of the wafer. After etching is complete,
the protective layer of photoresist is removed to reveal electrically
conducting or electrically insulating segments in the pattern determined by
the mask. Each additional layer put on the chip has a distinctive pattern
of this kind.
Adding Layers
Further masking and etching steps deposit patterns of additional materials
on the chip. These materials include polysilicon as well as various oxides
and metal conductors such as aluminum and tungsten. To prevent the
formation of undesired compounds during subsequent steps, other materials
known as diffusion barriers can also be added. On each layer of material,
masking and etching create a unique pattern of conducting and nonconducting
areas. Together these patterns aligned on top of one another form the
chip's circuitry in a three-dimensional structure. But the circuitry needs
fine-tuning to work properly. The tuning is provided by doping.
Doping
Doping deliberately adds chemical impurities, such as boron or arsenic, to
parts of the silicon wafer to alter the way the silicon in each doped area
conducts electricity. Machines called ion implanters are often used to
inject these impurities into the chip.
In electrical terms, silicon can be either n-type or p-type, depending on
the impurity added. The atoms in the doping material in n-type silicon have
an extra electron that is free to move. Some of the doping atoms in p-type
silicon are short an electron and so constitute what is called a hole.
Where the two types adjoin, the extra electrons can flow from the n-type to
the p-type to fill the holes.
This flow of electrons does not continue indefinitely. Eventually the
positively charged ions left behind on the n-type side and the negatively
charged ions on the p-type side together create an electrical force that
prevents any further net flow of electrons from the n-type to the p-type
region.
The material at the base of the chip is p-type silicon. One of the etching
steps in the manufacture of a chip removes parts of the polysilicon and
silicon dioxide layers put on the pure silicon base earlier, thus laying
bare two strips of p-type silicon. Separating them is a strip that still
bears its layer of conducting polysilicon; it is the transistor's 'gate.'
The doping material now applied to the two strips of p-type silicon
transforms them into n-type silicon. A positive charge applied to the gate
attracts electrons below the gate in the transistor's silicon base. These
electrons create a channel between one n-type strip (the source) and the
other (the drain). If a positive voltage is applied to the drain, current
will flow from source to drain. In this mode, the transistor is 'on.' A
negative charge at the gate depletes the channel of electrons, thereby
preventing the flow of current between source and drain. Now the transistor
is 'off.' It is by means of switching on and off that a transistor
represents the arrays of 1 and 0 that constitute the binary code, the
language of computers.
Done many times in many layers, these operations provide the chip with its
multitude of transistors. But just as provision must be made to run
electrical wires and plumbing pipes between floors of a building, provision
must be made in chips for interconnecting the transistors so they form an
integrated circuit.
Interconnections
This final step begins with further masking and etching operations that
open a thin layer of electrical contacts between layers of the chip. Then
aluminum is deposited and patterned using photolithography to create a form
of wiring that links all the chip's transistors. Aluminum is chosen for
this application because it makes good electrical contact with silicon and
also bonds well to silicon dioxide.
This step completes the processing of the wafer. Now the individual chips
are tested to ensure that all their electrical connections work using tiny
electrical probes. Next, a machine called a dicer cuts up the wafer into
individual chips, and the good chips are separated from the bad. The good
chips—usually most of the wafer's crop—are mounted onto packaging units
with metal leads. Wire bonders then attach these metal leads to the chips.
The electrical contacts between the chip's surface and the leads are made
with tiny gold or aluminum wires about 0.025 millimeter (0.001 inch) in
diameter. Once the packaging process is complete, the finished chips are
sent to do their digital work.







Computer Circuit Board
Integrated circuits (ICs) make the microcomputer possible; without them,
individual circuits and their components would take up far too much space
for a compact computer design. Also called a chip, the typical IC
consists of elements such as resistors, capacitors, and transistors
packed on a single piece of silicon. In smaller, more densely-packed ICs,
circuit elements may be only a few atoms in size, which makes it possible
to create sophisticated computers the size of notebooks. A typical
computer circuit board features many integrated circuits connected
together.


Circuit Board
Circuit boards, such as the one pictured here, are composed of integrated
circuits, resistors, capacitors, and other electronic components, connected
by conducting paths. Circuit boards of varying complexity are used in a
wide range of products including automobiles, televisions, stereo systems,
and computer


PRINTED CIRCULT BOARD (PCB)
Printed cct board is a device that has printed cct. PCB usually
eliminates the bulky wiring and tie points in a cct. This development of
PCB has reduced the size of the electronic equipment.



Printed Circuit Board
A printed circuit board consists of a sheet of non-conducting material to
which electronic components are attached. Conducting pathways between
components are stamped onto the boards.


LOGIC CIRCUITS.
LOGIC GATE- this is an electronic cct which makes a logic decisions. It
has one output and one or more inputs. 0s and 1


TYPES OF LOGIC CCTS
1. OR GATE
2. AND GATE
3. NOR GATE
4. NAND GATE
5. NOT GATE
THE ONLY TRUTH TABLE

Digital Circuits and Boolean Truth Tables


Digital circuits operate in the binary number system, which means that all
circuit variables must be either 1 or 0. The algebra used to solve problems
and process information in digital systems is called Boolean algebra; it
deals with logic, rather than calculating actual numeric values. Boolean
algebra is based on the idea that logical propositions are either true or
false, depending on the type of operation they describe and whether the
variables are true or false. "True" corresponds to the digital value of 1,
while "false" corresponds to 0. These diagrams show various electronic
switches, called gates, each of which performs a specific Boolean
operation. There are three basic Boolean operations, which may be used
alone or in combination: logical multiplication (AND gate), logical
addition (OR gate), and logical inversion (NOT gate). The accompanying
tables, called truth tables, map all of the potential input combinations
against yielded outputs.



THE INTERNAL STRUCTURE OF AN IC
Digital Logic and NOR Gate Circuitry
Computers use digital logic to perform operations. Digital logic involves
making successive "true" or "false" decisions, which may also be
represented by 1 and 0, respectively. Logic circuits, which are at the
heart of computer chips, are designed to make a series of these decisions
via junctures called gates. Gates are designed and arranged to make
different kinds of "decisions" about the input they receive. Individual
input and output values are always either true or false and are relayed
through the circuit in the form of different voltages. This circuit uses 4
NOR gates, each of which makes the decision "neither A nor B." The NOR
operation yields an output of 0 whenever one or more of the input values is
1. The table shows input values (A, B) and output value (F) for the NOR
gate. A circuit map (bottom) shows the layout of a NOR gate and its
components, indicating voltage values when the inputs are 0,0 and the
output is 1.

Dual In-Line Package
The dual in-line package, or DIP, is a premanufactured chip with downward-
pointing pins that can be soldered or plugged into a circuit board, making
board assembly easier.

N-P Junction
An n-p junction (also known as a diode) will only allow current to flow in
one direction. The electrons from the n-type material can pass to the right
through the p-type material, but the lack of excess electrons in the p-type
material will prevent any flow of electrons to the left. Note that the
current is defined to flow in a direction that is opposite to the direction
of the flow of the electrons.


Kirchhoff's Rules
Kirchoff's rules govern the flow of current and voltage through an electric
circuit. In this diagram, i stands for electric current and U stands for
voltage. Boldface letters designate parts of the circuit: R designates a
resistor, C a capacitor, and L an inductor. The smaller letters A, B, C, D,
E, and F simply correspond to points on the circuit. The junction rule
states that the sum of currents going into a junction (where the circuit
splits) must be equal to the sum of currents going out of the junction. The
loop rule states that the sum of voltages over a closed circuit must be
zero.

Computer System
A typical computer system consists of a central processing unit (CPU),
input devices, storage devices, and output devices. The CPU consists of an
arithmetic/logic unit, registers, control section, and internal bus. The
arithmetic/logic unit carries out arithmetical and logical operations. The
registers store data and keep track of operations. The control unit
regulates and controls various operations. The internal bus connects the
units of the CPU with each other and with external components of the
system. For most computers, the principal input devices are a keyboard and
a mouse. Storage devices include hard disks, CD-ROM drives, and random
access memory (RAM) chips. Output devices that display data include
monitors and printers.
.The physical computer and its components are known as hardware. Computer
hardware includes the memory that stores data and program instructions; the
central processing unit (CPU) that carries out program instructions; the
input devices, such as a keyboard or mouse, that allow the user to
communicate with the computer; the output devices, such as printers and
video display monitors, that enable the computer to present information to
the user; and buses (hardware lines or wires) that connect these and other
computer components. The programs that run the computer are called
software. Software generally is designed to perform a particular type of
task—for example, to control the arm of a robot to weld a car's body, to
write a letter, to display and modify a photograph, or to direct the
general operation of the computer.



" " " The "
" " "Operating System "


When a computer is turned on it searches for instructions in its memory.
These instructions tell the computer how to start up. Usually, one of the
first sets of these instructions is a special program called the operating
system, which is the software that makes the computer work. It prompts the
user (or other machines) for input and commands, reports the results of
these commands and other operations, stores and manages data, and controls
the sequence of the software and hardware actions. When the user requests
that a program run, the operating system loads the program in the
computer's memory and runs the program. Popular operating systems, such as
Microsoft Windows and the Macintosh system (Mac OS), have graphical user
interfaces (GUIs)—that use tiny pictures, or icons, to represent various
files and commands. To access these files or commands, the user clicks the
mouse on the icon or presses a combination of keys on the keyboard. Some
operating systems allow the user to carry out these tasks via voice, touch,
or other input methods.




COMPUTER MEMORY
Inside a Computer Hard Drive
The inside of a computer hard disk drive consists of four main components.
The round disk platter is usually made of aluminum, glass, or ceramic and
is coated with a magnetic media that contains all the data stored on the
hard drive. The yellow armlike device that extends over the disk platter is
known as the head arm and is the device that reads the information off of
the disk platter. The head arm is attached to the head actuator, which
controls the head arm. Not shown is the chassis which encases and holds all
the hard disk drive components. To process information electronically, data
are stored in a computer in the form of binary digits, or bits, each having
two possible representations (0 or 1). If a second bit is added to a single
bit of information, the number of representations is doubled, resulting in
four possible combinations: 00, 01, 10, or 11. A third bit added to this
two-bit representation again doubles the number of combinations, resulting
in eight possibilities: 000, 001, 010, 011, 100, 101, 110, or 111. Each
time a bit is added, the number of possible patterns is doubled. Eight bits
is called a byte; a byte has 256 possible combinations of 0s and 1s. See
also Expanded Memory; Extended Memory.
A byte is a useful quantity in which to store information because it
provides enough possible patterns to represent the entire alphabet, in
lower and upper cases, as well as numeric digits, punctuation marks, and
several character-sized graphics symbols, including non-English characters
such as π. A byte also can be interpreted as a pattern that represents a
number between 0 and 255. A kilobyte—1,024 bytes—can store about 1,000
characters; a megabyte can store about 1 million characters; a gigabyte can
store about 1 billion characters; and a terabyte can store about 1 trillion
characters. Computer programmers usually decide how a given byte should be
interpreted—that is, as a single character, a character within a string of
text, a single number, or part of a larger number. Numbers can represent
anything from chemical bonds to dollar figures to colors to sounds.
The physical memory of a computer is either random access memory (RAM),
which can be read or changed by the user or computer, or read-only memory
(ROM), which can be read by the computer but not altered in any way. One
way to store memory is within the circuitry of the computer, usually in
tiny computer chips that hold millions of bytes of information. The memory
within these computer chips is RAM. Memory also can be stored outside the
circuitry of the computer on external storage devices, such as magnetic
floppy disks, which can store about 2 megabytes of information; hard
drives, which can store gigabytes of information; compact discs (CDs),
which can store up to 680 megabytes of information; and digital video discs
(DVDs), which can store 8.5 gigabytes of information. A single CD can store
nearly as much information as several hundred floppy disks, and some DVDs
can hold more than 12 times as much data as a CD.
" " " "
" " "The Bus"


The bus enables the components in a computer, such as the CPU and the
memory circuits, to communicate as program instructions are being carried
out. The bus is usually a flat cable with numerous parallel wires. Each
wire can carry one bit, so the bus can transmit many bits along the cable
at the same time. For example, a 16-bit bus, with 16 parallel wires, allows
the simultaneous transmission of 16 bits (2 bytes) of information from one
component to another. Early computer designs utilized a single or very few
buses. Modern designs typically use many buses, some of them specialized to
carry particular forms of data, such as graphics.





HOW COMPUTER ARE MADE




The microprocessor is one type of ultra-large-scale integrated circuit.
Integrated circuits, also known as microchips or chips, are complex
electronic circuits consisting of extremely tiny components formed on a
single, thin, flat piece of material known as a semiconductor. Modern
microprocessors incorporate transistors (which act as electronic
amplifiers, oscillators, or, most commonly, switches), in addition to other
components such as resistors, diodes, capacitors, and wires, all packed
into an area about the size of a postage stamp.
A microprocessor consists of several different sections: The
arithmetic/logic unit (ALU) performs calculations on numbers and makes
logical decisions; the registers are special memory locations for storing
temporary information much as a scratch pad does; the control unit
deciphers programs; buses carry digital information throughout the chip and
computer; and local memory supports on-chip computation. More complex
microprocessors often contain other sections—such as sections of
specialized memory, called cache memory, to speed up access to external
data-storage devices. Modern microprocessors operate with bus widths of 64
bits (binary digits, or units of information represented as 1s and 0s),
meaning that 64 bits of data can be transferred at the same time.
A crystal oscillator in the computer provides a clock signal to coordinate
all activities of the microprocessor. The clock speed of the most advanced
microprocessors allows billions of computer instructions to be executed
every
ULSI (ultra-large-scale integration), term used for integrated circuits
manufactured with technology that makes it possible to fit over 100,000
components, such as transistors, on a single integrated circuit, or
microchip. All components on a ULSI microchip are so small they cannot be
seen without a microscope
Uses of digital computers
Archives consist of articles that originally appeared in Collier's Year
Book (for events of 1997 and earlier) or as monthly updates in Encarta
Yearbook (for events of 1998 and later). Because they were published
shortly after events occurred, they reflect the information available at
that time. Cross references refer to Archive articles of the same year.
1966: Electronics
The biggest newsmakers in electronics were the burgeoning fields of
microelectronics and high-speed digital computers, the latter with a
particular emphasis on medicine. Other electronic devices also made news in
medical electronics, with auto safety and crime prevention taking a share
of the electronics headlines.
Microelectronics.
Almost every major manufacturer of electronic equipment, ranging from
computers to industrial testing devices and consumer products, is actively
pursuing the application of microelectronics, or integrated circuits, to
its new designs. An integrated circuit, which would be dwarfed by a lump of
sugar, can do the work of a large number of electron tubes or transistors
and other electronic components. The majority of devices have been used in
digital computer applications, where repetitive functions demand the use of
tens of thousands of identical circuits.
Integrated circuit applications in electronic equipment date back to 1960,
when Westinghouse designed a communications receiver 35 times lighter and
smaller than the same set using equivalent standard-sized components. In
1961 Texas Instruments developed for the Air Force a telemetry encoder,
using 285 integrated circuits, which resulted in a 95 percent reduction in
size and weight over equivalent transistorized equipment.
However, the first major system to capitalize fully on the new
microelectronic technology was the Air Force's Minuteman 2 ICBM program in
1962. An improved intercontinental ballistic missile was needed to deliver
a heavier payload over a longer distance. Rather than become involved in an
expensive and time-consuming program to develop a more efficient propulsion
system, it was decided to reduce the size and weight of the electronic
guidance package. Two years later, the Minuteman 2 guidance system—using
integrated circuits—was successfully tested. A $9 million contract for
integrated circuits for Minuteman 2 was subsequently released by the Air
Force, and almost 500,000 circuits were purchased for use in guidance
computers and flight control and ground support equipment.
Recent integrated-circuit applications in weapons system design include:
(1) more than 6,000 devices for each fire-control computer used in the
Phoenix air-to-air missile system; (2) a large quantity of microelectronic
units for the Navy's Mark 48 torpedo control; (3) 3,000 integrated circuits
for each Univac airborne computer carried by Navy aircraft for
antisubmarine warfare; (4) 8,000 integrated circuits for each tactical data
system built for the Marine Corps; and (5) 8,000 integrated circuits for
each Army AN/GXC facsimile equipment and TF-600 forward area secure
communications system.
Price reductions in integrated circuits have prompted manufacturers of
electronic instruments to incorporate these devices in new designs. Weight
and volume have been reduced and reliability improved. Unexpected benefits
also have been gained in the form of lowered cost compared to the same
design using individual standard-sized components. For example, a 30
percent reduction was obtained in the cost of a Raytheon-built multiplexer
and digital-to-analog converter. An outstanding example of assembly
simplification is a desk-top electronic calculator developed by the Victor
Comptometer Corporation. This compact machine adds, subtracts, multiplies,
and divides and then displays the results on a built-in 4 × ½-inch
illuminated screen. Numerals of up to 20 digits can be handled with storage
and retrieval available with keyboard control. The unit is about the same
size as an electric typewriter and uses only 29 metal-oxide semiconductor
(MOS) integrated circuits.
Integrated circuits in consumer electronics first appeared in a hearing aid
developed by the Zenith Corporation in late 1963. Since then, considerable
research time has been devoted to microelectronics by the radio and
television industry. The first result was announced in early 1966 by the
Radio Corporation of America (RCA) Home Instrument Division. A four-
function monolithic integrated circuit was developed for use in the sound
section of their portable television receivers. One tiny silicon chip
replaced nearly 30 discrete parts and performed amplification, limiting, FM
detection, and audio pre-amplification functions.
The applications for integrated circuits in consumer products are quite
exciting. One possibility is an electronic wristwatch with digital display
of time combining microelectronic technology with electroluminescent
displays. More than 50,000 electronic organs are built each year, using
millions of transistors; assembly time and component cost will be reduced
substantially by the use of integrated circuits. Another product under
development is a tiny remote control system using microelectronics to dim
or raise the lighting level of each room in a home.
Computers in Medicine.
Computers have already been installed in many hospitals to handle the
staggering jobs of billing, filing, and recording. But more sophisticated
uses for the computers are already in experimental operation. For small
communities devoid of a trained cardiologist, it is common practice for the
local physician to mail a patient's electrocardiogram to a specialist and
wait several days for a detailed reply. The waiting time can be reduced to
minutes by having the patient's electrocardiogram translated into computer
language, fed via telephone data link to a centrally located medical unit,
analyzed by a computer, checked by a cardiologist in attendance, and
returned via the telephone data link. An International Business Machines
(IBM) Corporation 1401 data processing system used with more than 300
patients at Mount Sinai Hospital in New York has had an accuracy that
compares favorably with that of the best electro-cardiographers in the
field.
Computers can analyze the numerous facts relevant to a particular allergy
and prescribe the proper treatment within seconds; an experienced allergist
requires at least an hour. A computer program developed at the Mayo Clinic
can deliver results of a printed personality evaluation test in less than a
minute; a staff psychiatrist or psychologist formerly spent close to an
hour to compile each test result. A computer-controlled system in one
hospital provides the results of 1,000 blood tests an hour compared to 60
delivered by a highly skilled lab technician.
Perhaps the most promising of all efforts linking the computer with
medicine is in the area of diagnosis. Physicians cannot possibly find the
time to keep up with the voluminous amount of medical literature, research
advances, and new drugs. A national—and perhaps even worldwide—computer
center is under consideration to house data, statistics, and literature
abstracts. Under such an arrangement, a physician, clinic worker, or
medical research scientist could contact the center by telephone or data
link and supply a list of symptoms. He could then request specific
information to identify a particular disease and even be supplied with
latest medical literature and drug data to cope with the problem.
Medical Electronics
Electronic devices other than the large-scale computer that have assisted
the medical profession are the radio pill and cardiac pacemaker. The radio
pill is an ultra-compact FM transmitter encapsulated in a plastic tube the
size of a common cold pill. The pill is swallowed by the patient and the
signals that are transmitted enable the physician to chart the patient's
digestive tract. The cardiac pacemaker is another small electronic assembly
which applies properly timed electrical impulses to the heart when the
patient's natural action misses or falters. During lengthy heart surgery,
an external artificial heart—abundant with electronic circuits—is used to
bypass the patient's own heart and fulfill the organ's functions.
Two new diagnostic aids have been developed by medical electronic
researchers to combat heart disease. Both are designed to spot heart
abnormalities in the early stage, while chances for treatment and
successful surgery are high. One enables the physician to detect
pericardial effusion, a specific symptom linked to heart failure. The
second aid involves a new electronic treatment that can pinpoint a variety
of abnormal heart sounds.
Pericardial effusion is evidenced by the presence of fluid around the
heart. Previously, this condition was traced by puncturing the membrane
around the heart or else by circulating a material opaque to X rays to make
the heart show up in a radiograph. Both approaches were time-consuming and
troublesome. The pericardial effusion detector, developed at the University
of Rochester School of Medicine and Dentistry, requires an ultrasonic
transducer to be placed against the patient's chest. A portion of the sound
waves is reflected back to the transducer by the patient's body structure.
However, fluid around the heart has a different density from that of
surrounding tissues and alters the intensity of the echo reaching the
transducer. An oscilloscope displays the returned echo. The pattern
produced by a patient with a healthy heart is markedly different from that
shown when pericardial effusion is present.
A variety of heart abnormalities can be traced by a PhonoCardioScan,
marketed by Beckman Instruments. About the size of an attaché case, the
electronic instrument contains two electrodes and a microphone which are
attached to the patient's chest. The patient's heartbeat is converted into
electrical voltages which are compared with an electronic analog of a
normal heart's sound. The results of the comparison are presented in
digital form and indicate whether the patient's heartbeat is normal or not.
The examiner does not have to analyze the digital data; he can forward the
data by phone link for medical interpretation. This instrument is being
tested on 10,000 Chicago school children in a program sponsored by the U.S.
Public Health Service, the Illinois Department of Public Health, and the
Chicago Heart Association.
Electronics and Auto Safety.
With more than 50,000 people killed in automobile accidents in 1966, auto
safety campaigns have stirred the conscience of the American public. In the
United States, more than 96 million licensed drivers pilot about 87 million
vehicles, and over 870 billion miles of auto travel are carried over 3.6
million miles of highways, roads, and streets.
In an effort to find the 'why' of more than 12 million accidents reported
each year—involving about 22 million drivers—electronics is being used. The
major factor in auto accidents, the human behind the wheel, is being
closely studied with the aid of a driving simulator developed by RCA for
the U.S. Department of Health, Education and Welfare's Division of Accident
Prevention. The simulator consists of the shell of an automobile connected
to a 20-foot-long wooden tunnel. The inside of the car contains a standard
dashboard and steering assembly; however, outside light is blocked out by
wooden window boxes which provide illuminated scenes of highway traffic.
Through the windshield one can see a 20-foot roadway with five endless
belts. Two belts simulate two lanes of a highway, two belts simulate the
shoulders of the road, and the fifth belt represents the center lane. As
the belts are moved together, they create the illusion of highway travel.
An optical system combines this view with the illuminated pictures provided
by the wooden window boxes.
As the subject sits behind the wheel during a test, an unseen simulator
operator at a computer console can suddenly put other vehicles alongside
the driver, thus simulating conditions causing the majority of accidents.
Driver reaction response to various tests, when thousands of drivers are
involved in such tests, may lead to improvements in road and car design as
well as changes in traffic regulations.
Crime Prevention.
Computers and miniature electronic eavesdropping devices are new weapons
being used in the relentless effort to reduce crime. Criminals in the state
of California are now being tracked down by an electronic sleuth in the
form of a sophisticated data processing system. The general-purpose
computer stores records of criminal activities, data on registered
firearms, updated lists of lost, stolen, and pawned property, statistics on
drug addicts and narcotic activities, and detailed descriptions of the
modus operandi of criminals.
With such an electronic system, a police officer can isolate a list of
possible suspects by phoning a description to the computer center. To
illustrate the scope of this particular installation, in Sacramento more
than 8 million name cards— with real names and aliases—are filed, more than
6 million fingerprints are processed, and close to 1.7 million inquiries
are handled each year.
Another area receiving considerable attention from law-enforcement officers
involves electronic eavesdropping, or 'bugging.' Modern equipment includes
an FM bumper-mounted transmitter for surveillance of moving vehicles.
Magnets on the transmitter case fasten the device to the inside bumper
strip or to the underside of the auto chassis. Another device is a tiny AM
transmitter designed to be mounted within a radio or television cabinet.
The set's speaker is used as the pickup microphone, and the set's line cord
is used as the transmitting antenna. A third bug is an ultra-compact
telephone pickup amplifier using state-of-the-art microelectronic devices.
Perhaps the buggiest device is a 'spike-mike,' which can be driven into the
wall of a room adjacent to the one in which conversation is to be
monitored. Sound vibrations are picked up by the microphone and then
amplified for listening or tape recording.
Electronics in Project Apollo.
Man's first trip to the moon via the U.S. Apollo spacecraft represents a
massive challenge to the electronics industry. Complex, highly
sophisticated systems are being built, tested, and installed to accomplish
such critical functions as stabilization, guidance and navigation, and
communication. There will be little room for error or failure in any one of
these electronic systems, each of which is densely packed with hundreds of
thousands of electronic components.
Electronics will play several roles in the lunar mission. Guidance and
control of the Saturn booster stage during blast-off will be handled by a
combination of a ground-based computer and an electronic system housed in
the second stage of the booster. Once the craft is in orbit around the
earth, sensitive receivers and high-gain antennas at tracking stations
throughout the world will keep contact with the space vehicle. Precise
position information will be transmitted to the astronauts for insertion in
their space-borne guidance computer. Information from the computer will
determine the precise timing and duration of the booster refiring, as well
as the exact attitude and position at the time of the refiring, to hurl the
craft out of the earth's pull toward the moon. The astronauts and ground
stations will then quickly compare guidance data to assure proper
trajectory. Another group of electronic systems will aid in spacecraft
control, positioning of the Command and Service Module (CSM) relative to
the Lunar Excursion Module (LEM)—the vehicle which will descend to the
moon—and midcourse corrections. After two of the astronauts have descended
to the lunar surface in the LEM, leaving the CSM in orbit about the moon,
rendezvous between the CSM and LEM is accomplished with the help of
tracking radar. The two astronauts return in the LEM to join their
companion in the CSM. The LEM is detached and left in a lunar orbit. Headed
back to earth, the vehicle again depends on precise guidance and control
exercised by electronic systems. The dangerous and critical phase of re-
entry first involves precise control: If the vehicle enters the atmosphere
at a shallow angle, it will bounce off the atmosphere and disappear into
space; if entry is at too sharp an angle, the vehicle will burn up.
Applications Satellites.
Communication Satellite Corporation (COMSAT) planned to launch Aerocom in
1967 to provide voice communications for commercial aircraft flying the
Atlantic route, where conventional radio links are relatively poor.
Transmission of data from one computer installation to another thousands of
miles away is possible with communications satellites. Television
transmission of entertainment, interviews, and news events between United
States and Europe have already been carried by the Early Bird satellite and
its predecessors, Telstar, Relay, and Syncom.
Two other future applications of earth satellites are under development at
several leading electronics firms. Meteorological information from a
worldwide network of weather observation stations will be collected by a
chain of communications satellites. These data will be fed to a master
computer complex which will chart the weather pattern around the world.
Educational television programs can be transmitted from one satellite and
cover an area greater than several states. Schoolchildren in underdeveloped
countries could receive the finest in lectures and demonstrations at an
expense considerably lower than that needed to staff and supply hundreds of
small schoolhouses.
Dating by Computer.
The humming of computers turned to songs of love for college students
across the nation who applied to electronic matchmaking services, which
pair boys and girls with similar interests.
An applicant submits his answers to a variety of questions ('Do you believe
in a God who answers prayer?' 'Do you think romantic love is necessary for
successful marriage?'). In addition to describing his own characteristics,
he also indicates the qualities he desires in a dating partner. After
scanning the punch cards of thousands of lonely collegians, the computer is
able to provide the applicant with the names of five or more 'ideal
mates'—all for an application fee of a few dollars.
Making romance 'more efficient' was the idea of two Harvard undergraduates
who formed a corporation called Operation Match to improve the social life
of students at non-coed colleges and to reduce 'the anxiety of the blind
date.' Rival organizations sprang up at MIT (Contact) and at the University
of Wisconsin (SECS); TACT, a Manhattan organization aimed mainly at college
graduates in professional fields, also offers a series of 'compu-
functions,' including 'scientifically balanced cocktail parties.'

VLSI (very large-scale integration), term for integrated circuits
manufactured with technology that makes it possible to fit hundreds of
thousands of components, such as transistors, on a single integrated
circuit, or microchip. Some of the components on some VLSI microchips may
be so small that they cannot be seen without a microscope. Microchips with
even more components on them are called ULSI (ultra-large-scale
integration) integrated circuits.



DIP Switches
Dual in-line package (DIP) switches are devices used to control options on
a circuit board. Two common types of DIP switch are the rocker (left) and
the slide (right).





Uses of Electronic Devices
Electronic devices are used as tools in many areas of advanced research.
Shown here is a Scanning Electron Microscope which uses electrons to
produce a highly magnified image on a computer screen.
Lawrence Migdale/Photo Researchers, Inc.
Electronics, field of engineering and applied physics dealing with the
design and application of devices, usually electronic circuits, the
operation of which depends on the flow of electrons for the generation,
transmission, reception, and storage of information. The information can
consist of voice or music (audio signals) in a radio receiver, a picture on
a television screen, or numbers and other data in a computer.
Electronic circuits provide different functions to process this
information, including amplification of weak signals to a usable level;
generation of radio waves; extraction of information, such as the recovery
of an audio signal from a radio wave (demodulation); control, such as the
superimposition of an audio signal onto radio waves (modulation); and logic
operations, such as the electronic processes taking place in computers.
"I" "HISTORICAL BACKGROUND "
"I" " "


The introduction of vacuum tubes at the beginning of the 20th century was
the starting point of the rapid growth of modern electronics. With vacuum
tubes the manipulation of signals became possible, which could not be done
with the early telegraph and telephone circuit or with the early
transmitters using high-voltage sparks to create radio waves. For example,
with vacuum tubes weak radio and audio signals could be amplified, and
audio signals, such as music or voice, could be superimposed on radio
waves. The development of a large variety of tubes designed for specialized
functions made possible the swift progress of radio communication
technology before World War II and the development of early computers
during and shortly after the war.
The transistor, invented in 1948, has now almost completely replaced the
vacuum tube in most of its applications. Incorporating an arrangement of
semiconductor materials and electrical contacts, the transistor provides
the same functions as the vacuum tube but at reduced cost, weight, and
power consumption and with higher reliability. Subsequent advances in
semiconductor technology, in part attributable to the intensity of research
associated with the space-exploration effort, led to the development of the
integrated circuit. Integrated circuits may contain hundreds of thousands
of transistors on a small piece of material and allow the construction of
complex electronic circuits, such as those in microcomputers, audio and
video equipment, and communications satellites.
"II" "ELECTRONIC COMPONENTS "
"I " " "



Light-Emitting Diode (LED)
A diode is an electronic component through which current passes in only one
direction. Light-emitting diodes (LEDs) are semiconductors that produce
light when current passes through them. They are used in many common
devices, such as the tuning indicator on a radio. An arrangement of seven
LEDs in the shape of an '8' can be used to display any number from 0 to 9.
This arrangement is often used on calculators and digital watches.
Electronic circuits consist of interconnections of electronic components.
Components are classified into two categories—active or passive. Passive
elements never supply more energy than they absorb; active elements can
supply more energy than they absorb. Passive components include resistors,
capacitors, and inductors. Components considered active include batteries,
generators, vacuum tubes, and transistors.
"A" "Vacuum Tubes "



Vacuum Tube Amplifier
A vacuum tube amplifier circuit consists of a triode, load resister,
batteries, and variable voltage source. The triode is an evacuated glass
tube that consists of a cathode C, anode A, and grid G. Battery A heats the
filament in the cathode so that electrons are free to move. Battery B
maintains a potential difference between the cathode and anode and supplies
the energy that the electrons gain when they flow from the cathode to the
anode. This flow can be controlled by applying a negative voltage to the
grid with Battery C. The higher the negative voltage on the grid, the fewer
electrons flow from the cathode to the anode. Small changes in grid voltage
from a radio or audio signal S can produce large variations in current flow
from cathode to anode and throughout the rest of the circuit.
A vacuum tube consists of an air-evacuated glass envelope that contains
several metal electrodes. A simple, two-element tube (diode) consists of a
cathode and an anode that is connected to the positive terminal of a power
supply. The cathode—a small metal tube heated by a filament—frees electrons
, which migrate to the anode—a metal cylinder around the cathode (also
called the plate). If an alternating voltage is applied to the anode,
electrons will only flow to the anode during the positive half-cycle;
during the negative cycle of the alternating voltage, the anode repels the
electrons, and no current passes through the tube. Diodes connected in such
a way that only the positive half-cycles of an alternating current (AC) are
permitted to pass are called rectifier tubes; these are used in the
conversion of alternating current to direct current (DC) (see Electricity;
Rectification). By inserting a grid, consisting of a spiral of metal wire,
between the cathode and the anode and applying a negative voltage to the
grid, the flow of electrons can be controlled. When the grid is negative,
it repels electrons, and only a fraction of the electrons emitted by the
cathode can reach the anode. Such a tube, called a triode, can be used as
an amplifier. Small variations in voltage at the grid, such as can be
produced by a radio or audio signal, will cause large variations in the
flow of electrons from the cathode to the anode and, hence, in the
circuitry connected to the anode.
"B" "Transistor"
" " "s "



Circuit Board and Transistors
A close-up photograph of a smoke detector's circuit board reveals its inner
components, which include transistors, resistors, capacitors, diodes, and
inductors. The rounded silver containers house the transistors that make
the circuit work. Transistors are capable of serving many functions, such
as amplifier, switch, and oscillator. Each transistor consists of a small
piece of silicon that has been "doped," or treated with impurity atoms, to
create n-type and p-type semiconductors. Invented in 1940, transistors are
a fundamental component in nearly all modern electronic devices.
H. Schneebeli/Science Source/Photo Researchers, Inc.
Transistors are made from semiconductors. These are materials, such as
silicon or germanium, that are "doped" (have minute amounts of foreign
elements added) so that either an abundance or a lack of free electrons
exists. In the former case, the semiconductor is called n-type, and in the
latter case, p-type. By combining n-type and p-type materials, a diode can
be produced. When this diode is connected to a battery so that the p-type
material is positive and the n-type negative, electrons are repelled from
the negative battery terminal and pass unimpeded to the p-region, which
lacks electrons. With battery reversed, the electrons arriving in the p-
material can pass only with difficulty to the n-material, which is already
filled with free electrons, and the current is almost zero.
The bipolar transistor was invented in 1948 as a replacement for the triode
vacuum tube. It consists of three layers of doped material, forming two p-n
(bipolar) junctions with configurations of p-n-p or n-p-n. One junction is
connected to a battery so as to allow current flow (forward bias), and the
other junction has a battery connected in the opposite direction (reverse
bias). If the current in the forward-biased junction is varied by the
addition of a signal, the current in the reverse-biased junction of the
transistor will vary accordingly. The principle can be used to construct
amplifiers in which a small signal applied to the forward-biased junction
causes a large change in current in the reverse-biased junction.
Another type of transistor is the field-effect transistor (FET). Such a
transistor operates on the principle of repulsion or attraction of charges
due to a superimposed electric field. Amplification of current is
accomplished in a manner similar to the grid control of a vacuum tube.
Field-effect transistors operate more efficiently than bipolar types,
because a large signal can be controlled by a very small amount of energy.


"C" "Integrated "
" " "Circuits "



Integrated Circuit of a Computer
An integrated circuit (IC) consists of many circuit elements such as
transistors and resistors fabricated on a single piece of silicon or other
semiconducting material. The tiny microprocessor shown here is the heart of
the personal computer (PC). Such devices may contain several million
transistors and be able to execute over 100 million instructions per
second. The rows of leglike metal pins are used to connect the
microprocessor to a circuit board.
Most integrated circuits are small pieces, or "chips," of silicon, perhaps
2 to 4 sq mm (0.08 to 0.15 sq in) long, in which transistors are
fabricated. Photolithography enables the designer to create tens of
thousands of transistors on a single chip by proper placement of the many n-
type and p-type regions. These are interconnected with very small
conducting paths during fabrication to produce complex special-purpose
circuits. Such integrated circuits are called monolithic because they are
fabricated on a single crystal of silicon. Chips require much less space
and power and are cheaper to manufacture than an equivalent circuit built
by employing individual transistors.
"D" "Resistor"
" " "s "


If a battery is connected across a conducting material, a certain amount of
current will flow through the material (see Resistance). This current is
dependent on the voltage of the battery, on the dimensions of the sample,
and on the conductivity of the material itself. Resistors with known
resistance are used for current control in electronic circuits. The
resistors are made from carbon mixtures, metal films, or resistance wire
and have two connecting wires attached. Variable resistors, with an
adjustable sliding contact arm, are often used to control volume on radios
and television sets.
"E" "Capacitors"


Capacitors consist of two metal plates that are separated by an insulating
material (see Capacitor). If a battery is connected to both plates, an
electric charge will flow for a short time and accumulate on each plate. If
the battery is disconnected, the capacitor retains the charge and the
voltage associated with it. Rapidly changing voltages, such as caused by an
audio or radio signal, produce larger current flows to and from the plates;
the capacitor then functions as a conductor for the changing current. This
effect can be used, for example, to separate an audio or radio signal from
a direct current in order to connect the output of one amplifier stage to
the input of the next amplifier stage.
"F" "Inductors"


Inductors consist of a conducting wire wound into the form of a coil. When
a current passes through the coil, a magnetic field is set up around it
that tends to oppose rapid changes in current intensity (see Induction). As
a capacitor, an inductor can be used to distinguish between rapidly and
slowly changing signals. When an inductor is used in conjunction with a
capacitor, the voltage in the inductor reaches a maximal value for a
specific frequency. This principle is used in a radio receiver, where a
specific frequency is selected by a variable capacitor.
"G" "Sensing Devices and Transducers"


Measurements of mechanical, thermal, electrical, and chemical quantities
are made by devices called sensors and transducers. The sensor is
responsive to changes in the quantity to be measured, for example,
temperature, position, or chemical concentration. The transducer converts
such measurements into electrical signals, which, usually amplified, can be
fed to instruments for the readout, recording, or control of the measured
quantities. Sensors and transducers can operate at locations remote from
the observer and in environments unsuitable or impractical for humans.
Some devices act as both sensor and transducer. A thermocouple has two
junctions of wires of different metals; these generate a small electric
voltage that depends on the temperature difference between the two
junctions. A thermistor is a special resistor, the resistance of which
varies with temperature. A variable resistor can convert mechanical
movement into an electrical signal. Specially designed capacitors are used
to measure distance, and photocells are used to detect light (see
Photoelectric Cell). Other devices are used to measure velocity,
acceleration, or fluid flow. In most instances, the electric signal is weak
and must be amplified by an electronic circuit.
"IV" "POWER-SUPPLY CIRCUITS "


Most electronic equipment requires DC voltages for its operation. These can
be provided by batteries (see Battery) or by internal power supplies that
convert alternating current as available at the home electric outlet, into
regulated DC voltages. The first element in an internal DC power supply is
a transformer, which steps up or steps down the input voltage to a level
suitable for the operation of the equipment. A secondary function of the
transformer is to provide electrical ground insulation of the device from
the power line to reduce potential shock hazards. The transformer is then
followed by a rectifier, normally a diode. In the past, vacuum diodes and a
wide variety of different materials such as germanium crystals or cadmium
sulfide were employed in the low-power rectifiers used in electronic
equipment. Today silicon rectifiers are used almost exclusively because of
their low cost and their high reliability.
Fluctuations and ripples superimposed on the rectified DC voltage
(noticeable as a hum in a malfunctioning audio amplifier) can be filtered
out by a capacitor; the larger the capacitor, the smaller is the amount of
ripple in the voltage. More precise control over voltage levels and ripples
can be achieved by a voltage regulator, which also makes the internal
voltages independent of fluctuations that may be encountered at an outlet.
A simple, often-used voltage regulator is the zener diode. It consists of a
solid-state p-n-junction diode, which acts as an insulator up to a
predetermined voltage; above that voltage it becomes a conductor that
bypasses excess voltages. More sophisticated voltage regulators are usually
constructed as integrated circuits.
"V" "AMPLIFIER CIRCUITS "


Electronic amplifiers are used mainly to increase the voltage, current, or
power of a signal. A linear amplifier provides signal amplification with
little or no distortion, so that the output is proportional to the input. A
nonlinear amplifier may produce a considerable change in the waveform of
the signal. Linear amplifiers are used for audio and video signals, whereas
nonlinear amplifiers find use in oscillators, power electronics,
modulators, mixers, logic circuits, and other applications where an
amplitude cutoff is desired. Although vacuum tubes played a major role in
amplifiers in the past, today either discrete transistor circuits or
integrated circuits are mostly used.
"A" "Audio Amplifiers"


Audio amplifiers, such as are found in radios, television sets, citizens
band (CB) radios, and cassette recorders, are generally operated at
frequencies below 20 kilohertz (1 kHz = 1000 cycles/sec). They amplify the
electrical signal, which then is converted to sound in a loudspeaker.
Operational amplifiers (op-amps), built with integrated circuits and
consisting of DC-coupled, multistage, linear amplifiers are popular for
audio amplifiers.
"B" "Video Amplifiers"


Video amplifiers are used mainly for signals with a frequency spectrum
range up to 6 megahertz (1 MHz = 1 million cycles/sec). The signal handled
by the amplifier becomes the visual information presented on the television
screen, with the signal amplitude regulating the brightness of the spot
forming the image on the screen. To achieve its function, a video amplifier
must operate over a wide band and amplify all frequencies equally and with
low distortion. See Video Recording.
"C" "Radio Frequency Amplifiers"


These amplifiers boost the signal level of radio or television
communication systems. Their frequencies generally range from 100 kHz to 1
GHz (1 billion cycles/sec = 1 gigahertz) and can extend well into the
microwave frequency range.
"VI" "OSCILLATORS "



Oscillator Circuit
This illustration shows a simplified schematic diagram of an oscillator
circuit. The tuned circuit contains an inductor coil L1, a smaller inductor
coil L2, and a capacitor C.
© Microsoft Corporation. All Rights Reserved.
Oscillators generally consist of an amplifier and some type of feedback:
The output signal is fed back to the input of the amplifier. The frequency-
determining elements may be a tuned inductance-capacitance circuit or a
vibrating crystal. Crystal-controlled oscillators offer the highest
precision and stability. Oscillators are used to produce audio and radio
signals for a wide variety of purposes. For example, simple audio-frequency
oscillators are used in modern push-button telephones to transmit data to
the central telephone station for dialing. Audio tones generated by
oscillators are also found in alarm clocks, radios, electronic organs,
computers, and warning systems. High-frequency oscillators are used in
communications equipment to provide tuning and signal-detection functions.
Radio and television stations use precise high-frequency oscillators to
produce transmitting frequencies.
"VII" "SWITCHING AND TIMING CIRCUITS "



Digital Logic and NOR Gate Circuitry
Computers use digital logic to perform operations. Digital logic involves
making successive "true" or "false" decisions, which may also be
represented by 1 and 0, respectively. Logic circuits, which are at the
heart of computer chips, are designed to make a series of these decisions
via junctures called gates. Gates are designed and arranged to make
different kinds of "decisions" about the input they receive. Individual
input and output values are always either true or false and are relayed
through the circuit in the form of different voltages. This circuit uses 4
NOR gates, each of which makes the decision "neither A nor B." The NOR
operation yields an output of 0 whenever one or more of the input values is
1. The table shows input values (A, B) and output value (F) for the NOR
gate. A circuit map (bottom) shows the layout of a NOR gate and its
components, indicating voltage values when the inputs are 0,0 and the
output is 1.
Switching and timing circuits, or logic circuits, form the heart of any
device where signals must be selected or combined in a controlled manner.
Applications of these circuits include telephone switching, satellite
transmissions, and digital computer operations.
Digital logic is a rational process for making simple "true" or "false"
decisions based on the rules of Boolean algebra. "True" can be represented
by a 1 and "false" by a 0, and in logic circuits the numerals appear as
signals of two different voltages. Logic circuits are used to make specific
true-false decisions based on the presence of multiple true-false signals
at the inputs. The signals may be generated by mechanical switches or by
solid-state transducers. Once the input signal has been accepted and
conditioned (to remove unwanted electrical signals, or "noise"), it is
processed by the digital logic circuits. The various families of digital
logic devices, usually integrated circuits, perform a variety of logic
functions through logic gates, including "OR,""AND," and "NOT," and
combinations of these (such as "NOR," which includes both OR and NOT). One
widely used logic family is the transistor-transistor logic (TTL). Another
family is the complementary metal oxide semiconductor logic (CMOS), which
performs similar functions at very low power levels but at slightly lower
operating speeds. Several other, less popular families of logic circuits
exist, including the currently obsolete resistor-transistor logic (RTL) and
the emitter coupled logic (ELC), the latter used for very-high-speed
systems.

"VII" "RECENT DEVELOPMENTS "
"I " " "


The development of integrated circuits has revolutionized the fields of
communications, information handling, and computing. Integrated circuits
reduce the size of devices and lower manufacturing and system costs, while
at the same time providing high speed and increased reliability. Digital
watches, hand-held computers, and electronic games are systems based on
microprocessors. Other developments include the digitalization of audio
signals, where the frequency and amplitude of an audio signal are coded
digitally by appropriate sampling techniques, that is, techniques for
measuring the amplitude of the signal at very short intervals. Digitally
recorded music shows a fidelity that is not possible using direct-recording
methods. Digital playback devices of this nature have already entered the
home market. Digital storage could also form the basis of home video
systems and may significantly alter library storage systems, because much
more information can be stored on a disk for replay on a television screen
than can be contained in a book.
Medical electronics has progressed from computerized axial tomography, or
the use of CAT or CT scanners (see X Ray), to systems that can discriminate
more and more of the organs of the human body. Devices that can view blood
vessels and the respiratory system have been developed as well. Ultrahigh
definition television also promises to substitute for many photographic
processes, because it eliminates the need for silver.
Today's research to increase the speed and capacity of computers
concentrates mainly on the improvement of integrated circuit technology and
the development of even faster switching components. Very-large-scale
integrated (VLSI) circuits that contain several hundred thousand components
on a single chip have been developed. Very-high-speed computers are being
developed in which semiconductors may be replaced by superconducting
circuits using Josephson junctions (see Josephson Effect) and operating at
temperatures near absolute zero.
CMOS
CMOS, in computer science, acronym for complementary metal-oxide
semiconductor. A semiconductor device that consists of two metal-oxide
semiconductor field effect transistors (MOSFETs), one N-type and one P-
type, integrated on a single silicon chip. Generally used for RAM and
switching applications, these devices have very high speed and extremely
low power consumption. They are, however, easily damaged by static
electricity. See also Electronics.
Computer Memory, a mechanism that stores data for use by a computer. In a
computer all data consist of numbers. A computer stores a number into a
specific location in memory and later fetches the value. Most memories
represent data with the binary number system. In the binary number system,
numbers are represented by sequences of the two binary digits 0 and 1,
which are called bits (see Number Systems). In a computer, the two possible
values of a bit correspond to the on and off states of the computer's
electronic circuitry.
In memory, bits are grouped together so they can represent larger values. A
group of eight bits is called a byte and can represent decimal numbers
ranging from 0 to 255. The particular sequence of bits in the byte encodes
a unit of information, such as a keyboard character. One byte typically
represents a single character such as a number, letter, or symbol. Most
computers operate by manipulating groups of 2, 4, or 8 bytes called words.
Memory capacity is usually quantified in terms of kilobytes, megabytes, and
gigabytes. Although the prefixes kilo-, mega-, and giga-, are taken from
the metric system, they have a slightly different meaning when applied to
computer memories. In the metric system, kilo- means 1 thousand; mega-, 1
million; and giga-, 1 billion. When applied to computer memory, however,
the prefixes are measured as powers of two, with kilo- meaning 2 raised to
the 10th power, or 1,024; mega- meaning 2 raised to the 20th power, or
1,048,576; and giga- meaning 2 raised to the 30th power, or 1,073,741,824.
Thus, a kilobyte is 1,024 bytes and a megabyte is 1,048,576 bytes. It is
easier to remember that a kilobyte is approximately 1,000 bytes, a megabyte
is approximately 1 million bytes, and a gigabyte is approximately 1 billion
bytes.
" "[p"I"HOW MEMORY WORK "
" "ic] "I" "
" " "." "
" " " " "


Computer memory may be divided into two broad categories known as internal
memory and external memory. Internal memory operates at the highest speed
and can be accessed directly by the central processing unit (CPU)—the main
electronic circuitry within a computer that processes information. Internal
memory is contained on computer chips and uses electronic circuits to store
information (see Microprocessor). External memory consists of storage on
peripheral devices that are slower than internal memories but offer lower
cost and the ability to hold data after the computer's power has been
turned off. External memory uses inexpensive mass-storage devices such as
magnetic hard drives. See also Information Storage and Retrieval.
Internal memory is also known as random access memory (RAM) or read-only
memory (ROM). Information stored in RAM can be accessed in any order, and
may be erased or written over. Information stored in ROM may also be random-
access, in that it may be accessed in any order, but the information
recorded on ROM is usually permanent and cannot be erased or written over.
" " " " "
" " " "Internal RAM "


Random access memory is also called main memory because it is the primary
memory that the CPU uses when processing information. The electronic
circuits used to construct this main internal RAM can be classified as
dynamic RAM (DRAM), synchronized dynamic RAM (SDRAM), or static RAM (SRAM).
DRAM, SDRAM, and SRAM all involve different ways of using transistors and
capacitors to store data. In DRAM or SDRAM, the circuit for each bit
consists of a transistor, which acts as a switch, and a capacitor, a device
that can store a charge. To store the binary value 1 in a bit, DRAM places
an electric charge on the capacitor. To store the binary value 0, DRAM
removes all electric charge from the capacitor. The transistor is used to
switch the charge onto the capacitor. When it is turned on, the transistor
acts like a closed switch that allows electric current to flow into the
capacitor and build up a charge. The transistor is then turned off, meaning
that it acts like an open switch, leaving the charge on the capacitor. To
store a 0, the charge is drained from the capacitor while the transistor is
on, and then the transistor is turned off, leaving the capacitor uncharged.
To read a value in a DRAM bit location, a detector circuit determines
whether a charge is present or absent on the relevant capacitor.
DRAM is called dynamic because it is continually refreshed. The memory
chips themselves cannot hold values over long periods of time. Because
capacitors are imperfect, the charge slowly leaks out of them, which
results in loss of the stored data. Thus, a DRAM memory system contains
additional circuitry that periodically reads and rewrites each data value.
This replaces the charge on the capacitors, a process known as refreshing
memory. The major difference between SDRAM and DRAM arises from the way in
which refresh circuitry is created. DRAM contains separate, independent
circuitry to refresh memory. The refresh circuitry in SDRAM is synchronized
to use the same hardware clock as the CPU. The hardware clock sends a
constant stream of pulses through the CPU's circuitry. Synchronizing the
refresh circuitry with the hardware clock results in less duplication of
electronics and better access coordination between the CPU and the refresh
circuits.
In SRAM, the circuit for a bit consists of multiple transistors that hold
the stored value without the need for refresh. The chief advantage of SRAM
lies in its speed. A computer can access data in SRAM more quickly than it
can access data in DRAM or SDRAM. However, the SRAM circuitry draws more
power and generates more heat than DRAM or SDRAM. The circuitry for a SRAM
bit is also larger, which means that a SRAM memory chip holds fewer bits
than a DRAM chip of the same size. Therefore, SRAM is used when access
speed is more important than large memory capacity or low power
consumption.
The time it takes the CPU to transfer data to or from memory is
particularly important because it determines the overall performance of the
computer. The time required to read or write one bit is known as the memory
access time. Current DRAM and SDRAM access times are between 30 and 80
nanoseconds (billionths of a second). SRAM access times are typically four
times faster than DRAM.
The internal RAM on a computer is divided into locations, each of which has
a unique numerical address associated with it. In some computers a memory
address refers directly to a single byte in memory, while in others, an
address specifies a group of four bytes called a word. Computers also exist
in which a word consists of two or eight bytes, or in which a byte consists
of six or ten bits.
When a computer performs an arithmetic operation, such as addition or
multiplication, the numbers used in the operation can be found in memory.
The instruction code that tells the computer which operation to perform
also specifies which memory address or addresses to access. An address is
sent from the CPU to the main memory (RAM) over a set of wires called an
address bus. Control circuits in the memory use the address to select the
bits at the specified location in RAM and send a copy of the data back to
the CPU over another set of wires called a data bus. Inside the CPU, the
data passes through circuits called the data path to the circuits that
perform the arithmetic operation. The exact details depend on the model of
the CPU. For example, some CPUs use an intermediate step in which the data
is first loaded into a high-speed memory device within the CPU called a
register.
" " " "Internal ROM "


Read-only memory is the other type of internal memory. ROM memory is used
to store items that the computer needs to execute when it is first turned
on. For example, the ROM memory on a PC contains a basic set of
instructions, called the basic input-output system (BIOS). The PC uses BIOS
to start up the operating system. BIOS is stored on computer chips in a way
that causes the information to remain even when power is turned off.
Information in ROM is usually permanent and cannot be erased or written
over easily. A ROM is permanent if the information cannot be changed—once
the ROM has been created, information can be retrieved but not changed.
Newer technologies allow ROMs to be semi-permanent—that is, the information
can be changed, but it takes several seconds to make the change. For
example, a FLASH memory acts like a ROM because values remain stored in
memory, but the values can be changed.
" " " "External Memory "


External memory can generally be classified as either magnetic or optical,
or a combination called magneto-optical. A magnetic storage device, such as
a computer's hard drive, uses a surface coated with material that can be
magnetized in two possible ways. The surface rotates under a small
electromagnet that magnetizes each spot on the surface to record a 0 or 1.
To retrieve data, the surface passes under a sensor that determines whether
the magnetism was set for a 0 or 1. Optical storage devices such as a
compact disc (CD) player use lasers to store and retrieve information from
a plastic disk. Magneto-optical memory devices use a combination of optical
storage and retrieval technology coupled with a magnetic medium.
" " " " "
" " " "
" " " "

" " " "

" " " "
" " " "
" " " "
" " " "
" " " "
" " " "
" "Inside a Computer Hard Drive " "
" " " "
" "The inside of a computer hard disk drive consists of four main " "
" "components. The round disk platter is usually made of aluminum," "
" "glass, or ceramic and is coated with a magnetic media that " "
" "contains all the data stored on the hard drive. The yellow " "
" "armlike device that extends over the disk platter is known as " "
" "the head arm and is the device that reads the information off " "
" "of the disk platter. The head arm is attached to the head " "
" "actuator, which controls the head arm. Not shown is the chassis" "
" "which encases and holds all the hard disk drive components. " "
" " " "
" " " "
" " " "
" " " "
" " " "
" " " "
" " " "
" " " "
" " " "
" " " "
" " " "


Memory stored on external magnetic media include magnetic tape, a hard
disk, and a floppy disk. Magnetic tape is a form of external computer
memory used primarily for backup storage. Like the surface on a magnetic
disk, the surface of tape is coated with a material that can be magnetized.
As the tape passes over an electromagnet, individual bits are magnetically
encoded. Computer systems using magnetic tape storage devices employ
machinery similar to that used with analog tape: open-reel tapes, cassette
tapes, and helical-scan tapes (similar to video tape).
Another form of magnetic memory uses a spinning disk coated with magnetic
material. As the disk spins, a sensitive electromagnetic sensor, called a
read-write head, scans across the surface of the disk, reading and writing
magnetic spots in concentric circles called tracks.
Magnetic disks are classified as either hard or floppy, depending on the
flexibility of the material from which they are made. A floppy disk is made
of flexible plastic with small pieces of a magnetic material imbedded in
its surface. The read-write head touches the surface of the disk as it
scans the floppy. A hard disk is made of a rigid metal, with the read-write
head flying just above its surface on a cushion of air to prevent wear.
" " " "Optical "
" " " "Media "


Optical external memory uses a laser to scan a spinning reflective disk in
which the presence or absence of nonreflective pits in the disk indicates
1s or 0s. This is the same technology employed in the audio CD. Because its
contents are permanently stored on it when it is manufactured, it is known
as compact disc-read only memory (CD-ROM). A variation on the CD, called
compact disc-recordable (CD-R), uses a dye that turns dark when a stronger
laser beam strikes it, and can thus have information written permanently on
it by a computer.
" " " "Magneto-Optical Media"


Magneto-optical (MO) devices write data to a disk with the help of a laser
beam and a magnetic write-head. To write data to the disk, the laser
focuses on a spot on the surface of the disk heating it up slightly. This
allows the magnetic write-head to change the physical orientation of small
grains of magnetic material (actually tiny crystals) on the surface of the
disk. These tiny crystals reflect light differently depending on their
orientation. By aligning the crystals in one direction a 0 can be stored,
while aligning the crystals in the opposite direction stores a 1. Another,
separate, low-power laser is used to read data from the disk in a way
similar to a standard CD-ROM. The advantage of MO disks over CD-ROMs is
that they can be read and written to. They are, however, more expensive
than CD-ROMs and are used mostly in industrial applications. MO devices are
not popular consumer products.
" " " "Cache Memory "


CPU speeds continue to increase much more rapidly than memory access times
decrease. The result is a growing gap in performance between the CPU and
its main RAM memory. To compensate for the growing difference in speeds,
engineers add layers of cache memory between the CPU and the main memory. A
cache consists of a small, high-speed memory system that holds recently
used values. When the CPU makes a request to fetch or store a memory value,
the CPU sends the request to the cache. If the item is already present in
the cache, the cache can honor the request quickly because the cache
operates at higher speed than main memory. For example, if the CPU needs to
add two numbers, retrieving the values from the cache can take less than
one-tenth as long as retrieving the values from main memory. However,
because the cache is smaller than main memory, not all values can fit in
the cache at one time. Therefore, if the requested item is not in the
cache, the cache must fetch the item from main memory.
Cache cannot replace conventional RAM because cache is much more expensive
and consumes more power. However, research has shown that even a small
cache that can store only 1 percent of the data stored in main memory still
provides a significant speedup for memory access. Therefore, most computers
include a small, external memory cache attached to their RAM. More
important, multiple caches can be arranged in a hierarchy to lower memory
access times even further. In addition, most CPUs now have a cache on the
CPU chip itself. The on-chip internal cache is smaller than the external
cache, which is smaller than RAM. The advantage of the on-chip cache is
that once a data item has been fetched from the external cache, the CPU can
use the item without having to wait for an external cache access.
" " " "DEVELOPMENTS AND LIMITATIONS "


Since the inception of computer memory, the capacity of both internal and
external memory devices has grown steadily at a rate that leads to a
quadrupling in size every three years. Computer industry analysts expect
this rapid rate of growth to continue unimpeded. Computer engineers
consider it possible to make multigigabyte memory chips and disks capable
of storing a terabyte (one trillion bytes) of memory.
Some computer engineers are concerned that the silicon-based memory chips
are approaching a limit in the amount of data they can hold. However, it is
expected that transistors can be made at least four times smaller before
inherent limits of physics make further reductions difficult. Engineers
also expect that the external dimensions of memory chips will increase by a
factor of four, meaning that larger amounts of memory will fit on a single
chip. Current memory chips use only a single layer of circuitry, but
researchers are working on ways to stack multiple layers onto one chip.
Once all of these approaches are exhausted, RAM memory may reach a limit.
Researchers, however, are also exploring more exotic technologies with the
potential to provide even more capacity, including the use of biotechnology
to produce memories out of living cells. The memory in a computer is
composed of many memory chips. While current memory chips contain megabytes
of RAM, future chips will likely have gigabytes of RAM on a single chip. To
add to RAM, computer users can purchase memory cards that each contain many
memory chips. In addition, future computers will likely have advanced data
transfer capabilities and additional caches that enable the CPU to access
memory faster.
" " " "HISTORY "


Early electronic computers in the late 1940s and early 1950s used cathode
ray tubes (CRT), similar to a computer display screen, to store data. The
coating on a CRT remains lit for a short time after an electron beam
strikes it. Thus, a pattern of dots could be written on the CRT,
representing 1s and 0s, and then be read back for a short time before
fading. Like DRAM, CRT storage had to be periodically refreshed to retain
its contents. A typical CRT held 128 bytes, and the entire memory of such a
computer was usually 4 kilobytes.
International Business Machines Corporation (IBM) developed magnetic core
memory in the early 1950s. Magnetic core (often just called "core") memory
consisted of tiny rings of magnetic material woven into meshes of thin
wires. When the computer sent a current through a pair of wires, the ring
at their intersection became magnetized either clockwise or
counterclockwise (corresponding to a 0 or a 1), depending on the direction
of the current. Computer manufacturers first used core memory in production
computers in the 1960s, at about the same time that they began to replace
vacuum tubes with transistors. Magnetic core memory was used through most
of the 1960s and into the 1970s.
The next step in the development of computer memory came with the
introduction of integrated circuits, which enabled multiple transistors to
be placed on one chip. Computer scientists developed the first such memory
when they constructed an experimental supercomputer called Illiac-IV in the
late 1960s. Integrated circuit memory quickly displaced core and has been
the dominant technology for internal memory ever since.
GENERAL FEATURES OF THE FIRST GENERATION OF COMPUTER (1946-1954)
1 .the 1st generation of computer was the UNIVAC (universal automatic
computer)
2. Heat and maintenance are the problems with these machines.
3. It has limited internal storage capacitor.
4. input/output process is slow without the use of purched card.
5. These machine make use of VACCUM TUBE in electronics cct.
6. It uses symbol/assembly language in programming.
7. Use of purched card is very possible.
SOME OF THE EARLY SECOND GENERATION OF COMPUTER AND MACHINES WERE.
-IBM 700 SERIES.
-LEO MARK 111
-atlas (Manchester university uk1962. This made effective use of magnetic
disk storage.

SECOND GENERATION OF COMPUTER (1955-1964)
1. Transistors are used for internal operations.
2. There is an increase in primary storage capacitor.
3. Programming is made easier with the use of English like programming
language.
4. The use of magnetic disk storage is possible.
5. There is great reduction in size and heat generation.
THIRD GENERATION OF COMPUTER (1964-1971)
1. Use of integrated cct are made
2. There is an increase in storage capacity
3. The use of input/output process, there are more flexibility
4. Performance is better and reliable
5. Possibilities of the use of remote terminals


FOURTH GENERATION OF COMPUTER (1971-1980s)
1. Invention of micro processor, micro computer and super computer.
2. Development of computer software (program)
3. There is an increase in storage capacity and speed.


FIFTH GENERATION OF COMPUTER (1990-DATE)
1. They are marked with inputs coming from the human system in form of
speech natural language images and picture.
2. There is also effective processing of such inputs which comes from human
system
3. Computer here operates at an enormous speed and it has the ability to
make logical inferences
4. This generation of computer has emphasis on convensation or interactive
processing with suitable man machine interfaces.


COMPUTER NETWORKING



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