Fund a Notes

8/6/2019 Fund a Notes

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INTRODUCTION TO COMPUTERS

What is a Computer?

Computer is the most versatile electronic machine manhas ever created. Computers have made a great impact on our

day-to-day life. Their presence is felt in almost every walk of

life such as homes, schools, colleges, universities, offices,

industries, hospitals, banks, railways, airways, researches,

retail stores etc.

The word “computer” comes from the word “compute”,

which means to calculate. Hence, a computer is normally

considered to be a calculating device, which can perform

arithmetic operations at an enormous speed.

However, more than 80% of the work done by computers

today is of non-mathematical or non-numerical in nature (itcan do weather forecasting, reservations, maintain records,

monitor anesthesia in hospitals, help students for their study,

creating special effects in movies etc.). So, today we can’t say

it as only a calculating machine.

Prepared By: M.Aparna. 1



So, computer is an electronic device, which can

perform arithmetic operations and also take

logical decisions. In other words, a computer is

an electronic device which accepts the inputdata, stores the data, does the arithmetic and

logical computations in rapid speed and

outputs the required information in the desired

format.

Why Computers?

When we do a work manually, it takes a lot of time andwe want to save the time. For doing arithmetic and logical

operations, we have to use our brain and we want to avoid this

intellectual strain. While doing calculations, we often commit

mistakes and we want to avoid mistakes. We can’t remember

a data for a long time period but we want to store it for a long

period.

Due to the above reasons and many more, the developers

think about different machines, created them and the result is

“computer”.




Today, computer avoidance and computer ignorance are

practically impossible because it is the only machine which

very rapidly impact the world and also help human being in

every walk of life.

CHARACTERISTICS OF COMPUTERS:

The term computer characteristic means capabilities and

limitations of a computer system.

The characteristics are given below:

1. Speed: A computer can perform its operations/tasks/jobs

in fractions of a second. Imagine, what a computer can perform in one minute would take a person his/her entire

lifetime.

Speed of a computer, in earlier days is measured in terms

of milli seconds (10-3) and micro seconds (10-6). Now-a-days it

is measured in nano seconds (10-9) and in pico seconds (10-12).

2. Accuracy and Reliability: Today’s computers give 100%accurate results. Since it is very accurate, it is reliable. It is

estimated that a human being commits at least one error for

every 1000 operations. But computers do millions of

operations in a second committing no error.




3. Memory capacity: Computer has its memory to store a

huge amount of data. The data can be compactly stored in

computers and retrieved as and when required. As compared

to a human being who stores data only for a short time period,computers can remember all the data for several years. It

looses the data, if the user wants.

4. Capability to be programmed: A program is a set of

instructions by using a language to the computer. If a

computer is programmed once, then the same program can beexecuted as many times as we need.

5. Automation: A machine is said to be automatic, if it

works by itself without human intervention. Computers are

automatic, in the sense once started on a job; they carry on,

until the job is finished. However, they are only machines so

cannot start themselves.

6. Versatility: Computers can do varieties of applications.

It has no limitations for computer applications. If a problem

can be broken into a sequence of logical operations, then a

computer can be used to solve that problem. Computers are

used in banks, in the field of education, medicine i.e. in

different fields to work on different applications.

7. Diligence: Unlike human beings, a computer is free

from monotony, tiredness and lack of concentration. It can

perform a task repeatedly without showing any signs of




fatigue. If ten million calculations to be performed, a

computer will perform all with the same accuracy and speed

as of the first one. They do not sick days and take coffee

breaks even when work for long hours. If we program it once,

it can work as many times as we want with the same accuracyand efficiency.

The limitations are given below:

• 1. No I.Q.: A computer possesses no intelligence of its

own. Its I.Q. is zero at least until today. It has to be told

what to do and in what sequence.

•

2. GIGO: A computer has no knowledge about thecorrect or incorrect data as it is only a machine. So if the

user will input incorrect data to the computer, it also gives

incorrect information to the user. This phenomenon is

known as Garbage In Garbage Out (GIGO).

• 3. No feelings/experience: As they are machines,

they have no feelings, no emotions, and no instincts.

CLASSIFICATION OF COMPUTERS:

Computers can be classified in several ways. The general

methods of classification of computers are based on various

characteristics. Some important of them are given below:

a.) According to the purpose of use:

Computers can be classified into the following two

categories according to the purpose for which they are used:




1. Special Purpose Computers:

A computer which is used for particular/specific

work only is called a special purpose computer. They

have been designed or programmed at the time of

manufacturing for doing this particular task. Someexamples of special purpose computers are,

computers meant for ATM (Automatic Teller

Machine), traffic control, DTP (desktop publishing),

Robots etc.

2. General Purpose Computers:

A computer which is used for ordinary purposes andthe ability to do any type of work is called a general

purpose computer. Their software i

designed/installed by the user as per their

requirement. Most of the computers used in our day-

to-day work are of general purpose computers.

b.) According to the data on which it will operate:Computers can be classified into the following three

categories according to the data on which it will operate on:

1. Digital Computers:

These computers accept process and produce

discontinuous or digital data and perform

manipulation on numbers such as on binary digits 0

and 1. These are fast and give 100% accurate results.These computers do not operate on analog quantities

directly but if the user wants to process analog

quantities, these must be converted into digital data




before processing and for this purpose ADC (Analog-

to-Digital Converter) is used.

2. Analog Computers:

These computers accept process and producecontinuous data or analog data and perform

manipulation on physical quantities such as pressure,

temperature etc in form of voltages. These are faster

than digital computers but give 99% accurate results.

These computers do not operate on digital data

directly but if the user wants to process digital data,these must be converted into analog quantity before

processing and for this purpose DAC (Digital-to-

Analog Converter) is used.

3. Hybrid Computers:

These computers use good qualities of both digital

and analog computers. These are used for spaceresearch, process control and in medicals. It is used

in ICU (Intensive Care Unit) of hospitals to measure

the heart beat of a patient and give the result in

digital form to the doctor.

c.) According to the size and capability:




Computers can be classified into the following four

categories according to the size and capacity. Before that we

have to know about word of computer. A set of bits which hascapable of being stored in one storage location is called word

of a computer. The word length of computers will measured in

bits and varies from system to system. It may be of 8bits, 16

bits, 32 bits, 36 bits, 48 bits, 60bits, 64bits, 72 bits, 96 bits or

even 128 bits.

1. Micro Computers:

A micro computer is very small in size and it has the

lowest capability. Its word length is 8-16 bits and

today it is of 32 bits. A micro computer has a

microprocessor chip. Their capability is 100 KIPS

(i.e. Kilo Instructions Per Second). Two types of micro computers are in common use. They are

personal computers (PCs) and home computers

(HCs). Some of these are desktops, laptops etc. So

today what the computers we are using will fall under

this category.

2. Mini Computers:A mini computer is small in size and relatively has

more capability as compared to micro computers.

These computers have many peripherals (terminals

and key boards) but one CPU. Its word length is 8-16




bits and today it is of 32 bits. Their capability is 500

KIPS-1 MIPS (i.e. Million Instructions Per Second).

These are faster compared to micro computers and

used as multi-user systems.

3. Main-frame Computers:

A main frame computer is large in size and much

capability as compared to micro and mini computers.

These are also called as midi computers. Its word

length is 32-60 bits and today it is of 64 bits. Their

capability is 10 MIPS. These are also used in multi-user systems but as central host computers (or

servers). These can have the ability to hold a large

volume of data. Some main frame computers are

MEDHA, IBM, HP etc.

4. Super Computers:

A super computer is very large in size and muchcapability as compared to micro mini and midi

computers. These are also called as maxi computers.

Its word length is 64-96 bits and today it is of 128

bits. Their capability is 100 MIPS-10 BIPS (i.e.

Billion Instructions Per Second). These are used for

specific purposes (designing supersonic air crafts,

launching missiles, designing satellites, weather forecasting etc.). These can have the multiple CPUs

or multiple microprocessors. The cost of these

computers is in crores of rupees. Some super




computers are CRAY, CYBER, ANURAG etc. The

first indigenous super computer is PARAM.

EVOLUTION OF COMPUTERS:

“Necessity is the mother of invention”. This

holds true for computers, because computer is the onlymachine which impact human beings life very rapidly as

search for a fast and accurate calculating device. Gradually

the searching for a faster and accurate calculating machine

is now worked as a computer and the stages of development

is mentioned below:

The Mechanical Era:

In this mechanical age, men used wheels means gears,

pinions, axles etc. to build the machine for calculation

purpose. The first known mechanical calculating machine

PASCALINE was developed on the honor of its developer, a

French mathematician Blaise Pascal. This machine performs

addition, subtraction by rotating wheels. Then it is upgraded




by German mathematician Baron Gottfried Wilhelm von

Leibnitz to perform multiplication, division and to determine

square roots.

In 1822, Charles Babbage, an English Mathematiciandesigned a “Difference Engine” to do the calculations. Then in

1842, he came with a new idea and developed another

machine “ Analytical Engine” which was intended to be

completely automatic and uses technique to store data. It

contained all the essential components of a modern digital

computer such as I/O devices, storage area, processor etc. SoCharles Babbage is considered as the father of modern digital

computers.

Lady Ada Lovelace was working for Babbage’s project

and developed Binary number system for his machine and

writing programs for it. So Lady Ada Lovelace was

considered as the first computer programmer in the world.

In 1880, Herman Hollerith developed punched card to

store data. He developed a machine called tabulating machine

which read punched cards. His card has 12 rows and 80

columns. He founded the Tabulating Machine Company to

manufacture and sell his new inventions. And Later this

company merged with other companies and named as IBM(International Business Machine).

In 1944, Dr. Howard Aiken, a professor at Harvard

University designed the first fully automatic electro-




mechanical digital calculator called Automatic Sequence

Controlled Calculator and later popularized as Harvard Mark

I or simply Mark I . Although, it is extremely reliable, it was

very complex in design and huge in size. Physically, the

machine was 51 feet long and 8 feet high. It contains morethan 7, 50,000 parts strung together, 3000 electrical switches

to control with 500 miles of wire. The addition of two

numbers took 0.3 seconds and multiplication of two numbers

4.5 seconds. The magnitude of a number was restricted to 23

decimal digits.

The Electronic Era:

In this electronic age, men developed electronic

circuits and use them to build different machines for

calculation purpose. In 1942, the first electronic computer was

developed by Dr. John von Atanasoff and Cifford Berry and itwas named after its inventor’s name as Atanasoff-Berry

Computer (ABC). This was used to solve mathematical

equation and simulations. It uses 300 valves for the




calculation, 45 vacuum tubes for internal logic and capacitors

for storage.

In 1946, J. Presper Eckert and John Mauchly at MooreSchool of Engineering developed the first electronic calculator

named as ENIAC (Electronic Numerical Integrator And

Calculator). It performs the addition of two numbers in 200 µs

and multiplication in 2800 µs, so faster compared to MARK I.

But it was of 30 tons weight, 10 ft. wide, 10 ft. high and 100

ft. long and occupies 20 x 40 square ft. room and also usesnearly 18000 vacuum tubes to perform the calculation and its

programs were wired on boards.

Later in 1947, Dr. John von Neumann, a Hungarian

Mathematician was a consultant for the ENIAC project, gives

his giant idea i.e. stored program concept. “The basic idea behind this concept is that a sequence of instructions as well

as data can be stored in the memory of the computer for

automatically directing the flow of operations”. And this

concept influenced the development of modern digital

computer. He implemented this idea and developed EDVAC

(Electronic Discrete Variable Automatic Computer).

In 1949, Maurice Wilkes of USA developed EDSAC

(Electronic Delay Storage Automatic Calculator). It took1500




µs for the addition of two numbers and for multiplication 4000

µs.

In 1951, J. Presper Eckert and John Mauchly along with

John von Neumann developed an automatic digital computer

named UNIVAC (Universal Automatic Computer). UNIVAC isthe first automatic digital computer used for commercial

purpose.

GENERATIONS OF COMPUTERS

After 1940, technologies and so many computers were

developed rapidly. The development will give the trends in the

past and its projection in the future and termed as generation.

The entire important things about the different generations are

tabularized below:

Generatio

n

Period Main/Princip

le

Language




Electronic

Component

I st 1942 –

1954

Vacuum Tube Binary/Machine/

Low-Level

II nd 1955 – 1964

Transistor Assembly

III rd 1965 –

1974

IC (SSI and

MSI)

High-Level

(Procedure-

Oriented)

IV th 1975 –

At present

IC (LSI and

VLSI)

High-Level

(Object-Oriented)

V th Yet

not

come

(Under

R&D)

IC (ULSI) Ordinary/Natural

As we go through the history of evolution of computers,

we would find that the earliest computers were very big and,

because they were very big, they consumed a lot of power

and, because they consumed a lot of power, they heated up

tremendously and, because they heated up very quickly, they

had to be frequently shut down and cooled; because of all this

they were very expensive to build and maintain. As the

technology improved, computers became smaller and smaller.

They also became much more faster and more powerful. But

most importantly, from user’s point of view, they became




more affordable and user-friendly. And that has been the real

success of computer today.

**Depending upon the hardware and software used,

it is broadly classified into the following five generations:

First Generation (1942 – 1954):

In the first generation of computer vacuum tubes are used asthe principle component of computer. A vacuum tube is a

fragile glass device which uses filaments to control and

amplify electronic signals. These machines speed is measured

in milli-seconds. Binary/Machine/Low-Level language was

used and it is very difficult to learn, so only few people who

work with the machine understand the language.

These machines perform operations at a faster rate at thattime but were very expensive, too bulky or quite large in size,

non-portable, as thousands of vacuum tubes and other

components were used generate a lot of heat, require air

conditioning, consume very high power and chances of

hardware failure if filament will burn.

EDVAC, UNIVAC, IBM 360 and IBM 700 series (701,

704, 709) machines were of the first generation machines.




Second Generation (1955 – 1964):

In the second generation of computer transistors are used as

the principle component of computer. These machines speedis measured in micro-seconds. Assembly/Symbolic language

was used and it is not so difficult to learn, but requires

assemblers to do the conversion from assembly language to

binary language and vice versa, as the machine understands

only the binary language.

But compared to first generation machines these machines are

better. These machines perform operations at a faster rate but

were also expensive, quite large in size, non-portable, as

thousands of transistors and other components were used

generate a lot of heat, require air conditioning, consume high

power.

IBM (1401, 1620, 7090, 7094 I, 7094 II), PDP (1, 5, 8)

machines were of the second generation machines.

Third Generation (1965 – 1974):

In the third generation of computer ICs (Integrated

Circuits) are used as the principle component of computer. ICs




consisting of several electronic components like transistors,

resistors and capacitors placed on a single chip of silicon,

eliminating wired inter-connection between components. In

this generation depending upon the number of components

integrated into a single chip, Small Scale Integration i.e. SSI(1 to 100) and Medium Scale Integration i.e. MSI (100 to

1000) chips were used. These machines speed is measured in

nano-seconds. High-level but procedural languages (i.e.

FORTRAN, COBOL, PASCAL, BASIC, PL/1) were used,

but require translators (compilers and interpreters) to do the

conversion from high-level language to binary language andvice versa, as the machine understand only the binary

language.

But compared to previous two generation machines these

machines are better. These machines perform operations at a

faster rate and not so expensive, size was compacted, non-

portable. Still require air conditioning, consume less power.

IBM (360,370), TDC (316, 332), ICL 1900, PDP II, CDC

(7600, CYBER 175, STAR 100) machines were of the third

generation machines.




Fourth Generation (1975 – Till Today):

In the fourth generation of computer ICs (IntegratedCircuits) are used as the principle component of computer. In

this generation depending upon the number of components

integrated into a single chip, Large Scale Integration i.e. LSI

(1000 to 100000) and Very Large Scale Integration i.e. VLSI

(100000 to 1000000) chips was used. When so much chips are

integrated that is a million of components in a single chip, it iscalled as microprocessors. These machines speed is measured

in nano-seconds and even in pico-seconds. High-level but

object oriented languages (i.e. C++, JAVA, PROLOG) were

used, but require translators (compilers and interpreters) to do

the conversion from high-level language to binary language

and vice versa, as the machine understand only the binary

language.

But compared to previous three generation machines

these machines are better. These machines perform operations

at an imaginable faster rate and cheaper also available for

commercial purposes. Size of the machine was compacted to

reside in a table, portable. For cooling purpose fans are usedwith the cabinet, consume very less power.




IBM 4300, ICL 2900 and what are the HC’s (Home

Computers) and PC’s (Personal Computers), Laptops, we are

using today is of the fourth generation machines.

Fifth Generation (Yet Not Come):

Fifth generation computer is only a promise, but yet not

the reality. This project is given to the USA, JAPAN and UK.

They try to use the Ultra Large Scale Integration i.e. ULSI

chips in these machines. ULSI chips are those chips where 1

to 10 million of components integrated. The developers think to use the ordinary/natural language i.e. ENGLISH,

JAPANESE etc. in this fifth generation machines and

implementing the artificial intelligence (AI). So the

programmers will not have to learn programming language but

they only tell what to do not how to do. They have to

communicate with the machine through speech, images etc.




Overview of Computer Organization

The internal architecture of computers differs from one

system to another. However, the basic organization remains

the same.

All computer systems perform the following five basic

operations/processes:

Inputting: The process of entering/feeding data and

instructions into the computer system is called

inputting.

Storing: The process of saving/holding of data andinstructions in the memory so that they are available

for processing as and when required is called storing.

Processing: The process of performing operations (arithmetic

or logical) on data in order to convert them into

useful information is called processing.

Outputting: The process of producing/retrieving/showing

useful information/result to the user in printed formor on the visual display (screen/monitor) is called

outputting.




Controlling: The process of directing the manner and

sequence in which all of the above operations are

performed is called controlling.

Data flow lines

Control lines

A block diagram of the basic computer organization is

shown in the above figure. In this figure, the solid lines are

used to indicate the flow of data and instructions and the

dotted lines are used to indicate the control exercised by the


InputUnit

Arithmetic & Logic Unit

Control Unit

Memory Unit Output

Unit

Central Processing Unit(CPU)

Fig: Block Diagram of a Computer



control unit. It depicts the five major building blocks or

functional units of a digital computer system.

Basing on the above five basic operations, the computers

have five major functional units as mentioned below:

Input Unit (IU)

Memory Unit (MU)

Arithmetic and Logic Unit (ALU)

Output Unit (OU)Control Unit (CU)

CENTRAL PROCESSING UNIT (CPU):

It is known as the brain of the computer. Because as

compared to the brain of a human being, it also stores the data,

process the data and gives instruction to other units. The major

units available inside it will do all these. So, it makes all major

calculations, manipulations and comparisons. It is also

responsible for activating and controlling the operations

performed by all other units of the computer system. The

major units of it are:

• Arithmetic Logic Unit (ALU)

• Control Unit (CU)

• Memory Unit (MU)




Arithmetic Logic Unit (ALU): All calculations are performed

and all comparisons are made in the ALU. The data and

instructions, stored in the primary memory prior to processing,

are transferred to the ALU where actual processing takes place. Intermediate results generated in the ALU are

temporarily transferred back to the primary memory until

needed again. After completion of processing, the final results

also send back to the primary memory.

Control Unit: It acts as a central nervous system for theother components of the computer. It manages and coordinates

the entire computer system, including input and output units.

It fetches instructions from the main memory, decodes the

instruction and interprets the instruction to know what tasks

are to be performed. Then it sends suitable control signals to

other components to perform further necessary steps to

execute the instruction. It maintains order and directs theoperation of the entire system.

Memory Unit: The function of the memory is to store

information. The data and instructions that are entered into the

computer system through input units are stored inside the

computer before the actual processing starts. Similarly, the

results produced by the computer after processing are stored inthe computer before passed to the output units. Moreover, the

intermediate results produced by the computer must also be

stored for ongoing processing.




The memory capacity is measured by the following units

as mentioned below by the increased order:

Bit 1 bit (0 or 1)

Nibble 4 bits

Byte 8 bitsKilobyte (KB) 210 bytes/1024 bytes

Megabyte (MB) 220 bytes

Gigabyte (GB) 230 bytes

Terabyte (KB) 240 bytes

According to the performance of memories, it is of the

following three types. The below figure shows the memoryhierarchy in a computer.

i.) PRIMARY MEMORY:


Arithmeticand

Logic Unit

(Resistors)

Cache

Memory PrimaryMemory Secondary

Memory

Fig: Memory hierarchy in a computer system



It is a faster memory compared to

the secondary memory. It is also known as

main/volatile/temporary memory or Immediate Access

Store (IAS). These are volatile in nature i.e. the contents(the stored data or information) are lost/erased from the

memory when the power goes off. It has limited storage

capacity as it is costlier compared to secondary memories.

Its speed is measured in nano-seconds i.e. its access time

(i.e. time taken to retrieve information from the memory) is

about 50 ns (nanoseconds). The current applications, programs, operating system, compiler etc. (which we are

working with) are loaded into this primary memory.

ii.) SECONDARY MEMORY:

It is a slower memory compared tothe primary memory. It is also known as auxiliary/non-

volatile/permanent/backup memory. These are non-volatile

in nature i.e. the contents (the stored data or information)

are not lost/erased from the memory when the power goes

off. It has a huge storage capacity as it is cheaper compared

to primary memories. Its speed is measured in milli-seconds

i.e. its access time (i.e. time taken to retrieve informationfrom the memory) is about 5-10 ms (milliseconds). The

applications, programs, operating systems, compilers etc.

(which are installed) are stored in this secondary memory.




iii.) CACHE MEMORY:

It is the fastest memory compared

to primary and secondary memory. It has a limited storagecapacity as it is very expensive compared to other two

memories. Its speed is measured in nano-seconds i.e. its

access time (i.e. time taken to retrieve information from the

memory) is about 10 ns (nanoseconds). The cache memory

is not accessible to user. It stores instructions and data

which are to be immediately executed. To compensate thespeed mismatch between ALU and main memory, cache

memory is used. Its access time is closer to the processing

speed of the ALU.

**According to the material used for the construction of

memories, it is of the following three types.

A. SEMI-CONDUCTOR MEMORY:

It is made of semi-conducting materials i.e. flip-flops.

These types of memories are faster, lighter, costlier, smaller in size, low storage capacity and consume less power. The

semi-conductor memories are RAMs, ROMs, PDs etc.




RAM:

This is known as Random Access Memory. It

possesses random access property i.e. any memorylocation can be accessed in a random manner, so the

access time is same for each location. It is a volatile

memory, so used as the primary memory of a computer. It

comes in various capacities, for example, 64MB, 128MB,

256MB, 512MB, 1GB, 2GB etc.

There are two important types of RAMs: static RAM and

dynamic RAM.

Static RAM (SRAM) Dynamic RAM (DRAM)

1. SRAM can retain storedinformation as long as

the power supply is on.

2.These are costlier and

higher speed than

DRAMs.

3. These consume more

power.

4. SRAMs don’t need

refreshing circuitry.

5. Being faster, so

generally used as for

1.DRAM loses the storedinformation in a very short

time (in few milliseconds),

even though the power

supply is on.

2.These are cheaper and

have high packing density

and moderate speed.

3.These consume less

power.

4.DRAMs have to be

refreshed periodically, so




cache memory. need additional refreshing

circuitry.

5.Generally used as for

primary memory.

ROM:

This is known as Read Only Memory and non-

volatile in nature. It also possesses random access

property. ROMs are of two types: mask programmed

ROM and user programmed ROM .

Mask Programmed ROM:

It is called as only the ROM. Its contents are decided at

the manufacture time by the programmers. The bootstrap

program is loaded in ROM. The bootstrap program contains




the information of hardware functionality. So when machine is

booted/ restarted, the bootstrap program of ROM will be

loaded in RAM. It looks for the hardware attached to your

machine and whether they are functioning or not. Then search

for the operating system and if found loaded into RAM.Except these, ROM also holds the function tables such as sine,

cosine, square root, exponential, logarithm etc.

User Programmed ROM:

It is another type of ROM whose contents are not decidedat the manufacture time by the programmers. The contents of

this type of ROM are decided by the users. And some user

programmed ROMs are also modified. So below the various

user programmed ROMs are explained:

a.) PROM:

It stands for Programmable ROM. The contents

of this ROM will be decided by the users. Once

written into ROM, they cannot be modified. A

special equipment called PROM programmer is

available for the programming of PROMs.

b.) EPROM:

It stands for Erasable Programmable ROM. The

content of this type of ROM can be erased by some




means and again can be programmed. This is used for

research and development purpose as the developers

modifying and updating the data several times.

According to the means of erasing data, it is of two

types:

i.) EEPROM (E 2PROM): It stands for

Electrically Erasable Programmable ROM. It is

also known as Electrically Alterable

Programmable ROM (EAPROM) and also

called as flash memory. This type of EPROMcan be erased by passing electricity on to it.

ii.) UVEPROM: It stands for Ultra Violet

Erasable Programmable ROM. This type of

EPROM can be erased by exposing it into ultra

violet rays.

PD:

This is known as Pen Drive and non-volatile

in nature, so used as a permanent/back up memory. It also

possesses random access property. It is a small device, so

is portable and now-a-days commonly used. It is also

having large capacity and low price. It comes in various

sizes like 128 MB, 256MB, 512MB, 1GB, 2GB etc.

B. MAGNETIC MEMORY:




It is made of magnetic materials i.e. iron oxide or ferrite

core or chromium dioxide. These are generally of non-volatile

in nature, so used as secondary/back up memory. These types

of memories are slower, weighted, cheaper, larger in size,

huge capacity and consume more power. The magneticmemories are magnetic tape, magnetic disk (floppy disk, hard

disk) etc.

A. Magnetic Tape:

Magnetic tape is one of the most popular storagemediums for large volume of data. It possesses

sequential/serial access property i.e. information stored

and retrieved from it directly from a location is not

possible. To read/write of data from/into the tape is done

by placing the tape into the tape drive. Different types of

magnetic tapes are available like in form of ½ inch reel, ½

inch cartridge, ¼ inch tape, 4 mm or 8 mm digital audiotape (DAT).

The storage capacity of a tape is measured by the

following way:

Storage capacity of a tape = Data recording

density x Length of the tape

Characteristics:




a) Is a plastic ribbon usually ½ inch wide that is

coated on one side with an iron oxide material.

b)Ribbon itself is stored in reels of 50 to 2400 feet.

c) It is of high quality and durable.

d)Tape is divided into vertical columns called framesand horizontal rows called channels or tracks.

e) It can either read data from a tape into the CPU or

it can write the information being produced by the

computer onto a tape.

f) It can store about 40 million characters and can

read at a speed of 160000 character per second.

Advantages:

a)Unlimited storage.

b)High data density.

c)Low cost.

d)Rapid transfer rate.e)Ease of handling.

f) Portability.

Disadvantages:

a)No direct access.

b)Indirect interpretation.c)Environmental problems.




B. Magnetic Disk:

Magnetic disk is the most popular storage mediumfor large volume of data. It possesses random access

property. A magnetic disk is having a thin plate/platter,

made of metal or plastic which is usually coated on both

sides with iron oxide material. Data are recorded on the

disk in the form of tiny invisible magnetized and non-

magnetized spots (representing 1s and 0s) on the coatedsurface of the disk. The new data can be written into a

disk, so that the old data will be erased automatically.

Both side of the disk is used for writing data into it and

Read/Write head is mounted above each surface. To

read/write of data from/into the disk is done by placing

the disk into the disk drive.

For data recording, the surface of a disk is divided into a

number of invisible concentric circles, called tracks. In

addition to the concentric circles, the disk surface is also

divided into invisible pie-shaped segments called sectors.

A sector typically contains 512 bytes. Each track and each

sector of a disk is assigned a unique number. The storage

capacity of a disk is measured by the following way:

Storage capacity of a disk = Number of recording

surfaces * Number of tracks per surface




* Number of sectors per track* Number of

bytes per sector

Magnetic disks are of two types i.e. floppy disk and hard

disk .

I. Floppy Disk:

Floppy disk was introduced by IBM in 1972 for

portable and to reduce the cost. Floppy disks are so

called because they are made of flexible plastic

plates, which can be bend, not hard plates. These are

popularly known as floppies/diskettes. It is encased in

a square plastic or vinyl or cardboard jacket cover which protects it from dust particles.

Characteristics:

a)Made of flexible plastic that is coated with

magnetic oxide. b)Enclosed with in a square plastic or cardboard

jacket, which gives a handling protection to the

disk surface.




c)A hole is present in the center of the disk for index

mark sensing.

d)Information is recorded with the help of read write

heads.

e)These are available in two standard sizes 3.5,5.25inches.

f) It is both an input device and output device.

Advantages:

a)Cheaper.

b)Can be used as both input and output medium.

c)Very useful for portable computers.

d)Faster access medium.

Disadvantages:

a)Not useful for storing media or audio files.

b)Limited amount of space.

It is placed inside a device to perform read/write data

from/to it, is known as floppy disk drive. Floppy

disks come in various sizes and capacities by

manufacturers.

3½ (3.5) inch Floppy Disk:




It is so named because the diameter

of the disk is 3.5”. The jacket cover has a cutout for

the read/write head to make contact with the disk

surface. This part is covered with a sliding metal

shield. When the diskette is inserted into the drive,the metal shield slides aside to expose the disk

surface to the read/write head. There is a hole at the

center for drive spindle which rotates it. There is a

write-protect tab to protect the stored information

from viruses. It uses a sliding plastic button, which

can slide to either of the two positions. One positionallows reading, writing, erasing etc. the other position

allows only for reading. The button slides in a track.

When light is visible through the track, then only the

disk is write-protected. The storing capacity of this

floppy (high-density) is 1.44 MB.

5¼ (5.25) inch Floppy Disk:

It is so named because the diameter

of the disk is 5.25”. The jacket cover has an oval

shaped cutout for the read/write head to make contact

with the disk surface. There is a hole at the center for

drive spindle which rotates it. A plastic hub ring is

fitted at the center to protect the internal edge of thedisk. A black or silver adhesive tape is supplied with

each floppy, which is called write-protect notch to

protect the stored information from viruses. The storing

capacity of this floppy is 1.20MB. (It having 2




recording surfaces, 80 tracks/surface, 15 sectors/track,

512 bytes/sector, giving a total storage capacity of 2 x

80 x 15 x 512 = 1228800 bytes = 1200 KB = 1.2 MB.

Floppy Disk Drive:

A floppy disk drive is a device which is used

to read/write data from/to floppy disk. The drive has a

spindle (which rotates the disk) and read/write heads

(which can move in and out, to position the heads on any

track of the disk surface). The drive has a door throughwhich the floppy can be inserted by just slipping the disk

into the slot, floppy can be removed by pressing the eject

button on the drive. Here the heads come with direct

contact to the surfaces of the disk, so constant use worn

out the disks. The rotational speed of a floppy disk is with

300-400 rpm. The drives are also different for the two

types of disks (i.e. 3.5” and 5.25”).

II. Hard Disk:

Hard disks are on-line storage devices. The

term on-line means that the device is permanently

connected to the computer system. When computer power

is on, it is ready to store information or to give




information. These are used for mass storage purpose.

They store operating system, compilers, assemblers,

different software, databases etc. A hard disk is also

called as platter . The disk(s) are encased in a sealed, air

filtered, contamination free metal enclosure known ashard disk drive, which also holds the read/write heads.

Characteristics:

a)A hard disk pack consists of magnetic plates fixedto a spindle; one below the other with a set of read

write heads.

b)Permanently sealed in a casing to protect it from

dust.

c)Disk pack rotates at a speed of 3600 rpm.

d)Information recorded on the surface of a disk

because it rotates about its axis.e)A set of all tracks in all surfaces of a disk pack is

called a cylinder.

f) A cylinder consists of 10 tracks per disk, tracks are

divided into sectors 512 bytes of information is

stored per sector.

g)When the disk controller receives a read write

command, the read write heads reaches to thespecified cylinder.




Advantages:

a)Can hold large amount of information.

b)High reliability.

c)Low priced.d)Access time is very low.

Disadvantages:

a)Heavy and difficult to replace. b)Bit expensive then floppies.

Various types of hard disks are available:

a) Zip/Bernoulli Disk:




In this type, a single hard disk platter is encased

in a plastic cartridge. A commonly used zip disk is of

3½ inch size, having capacity of 100 MB. Its disk

drive is called zip drive, which may be portable or of

fixed type.

b) Disk Packs:

A disk pack consists of multiple (two or more)

hard disks platters mounted on a single central shaft.

The disk drive of a disk pack has a separate

read/write head for each disk surface, excluding the

upper surface of the topmost disk and lower surface

of the bottommost disk because those two surfaces

are not used for the recording purpose. This disk pack can be removed from the disk drive.

c)Winchester Disks:

A Winchester disk also consists of multiple (twoor more) hard disk platters mounted on a single shaft.

This pack is of fixed type i.e. the disk platters and the

disk drive are put together in a sealed container. Here

both sides of all disks can be recorded. Different

capacity of hard disks which supports thisPrepared By: M.Aparna. 41



Winchester technique is available such as 40 GB, 80

GB, 100 GB, 160 GB etc.

Hard Disk Drive:

A hard disk drive is a device which is used to

read/write data from/to hard disk(s). The drive has aspindle (which rotates itself and holds the disks) and

read/write heads for each disk surfaces (which can move

in and out, to position the heads on any track of the disk

surface). The rotational speed of the spindle is around

2400 rpm. Here the heads does not come with direct

contact to the surfaces of the disk, so constant use not

worn out the disks.

C. OPTICAL MEMORY:

It is made of optical materials i.e. fabric or resin,

made of polycarbonate. These are generally of non-volatile

in nature, so used as secondary/back up memory. These




types of memories are slower, lighter, cheaper, smaller in

size, very huge storage capacity, longer life and consume

very less power.

These disks are coated with a highly reflectivematerial, usually aluminum. Information is written to or

read from an optical disk using laser beam. Due to the use

of laser beam technology, optical disks are also known as

laser disks. The high intensity laser beam forms a tiny pit

along a trace to represent ‘1’ and the surface without a pit

(or the unaltered areas between the pits) is known as land to represent ‘0’. The reflected laser is sensed by a

photodiode to read data. The intensity of the reflected light

of laser changes as it encounters a pit. A pit spread the

light so that the photodiode receives less reflected light.

But land reflects sufficient light to the photodiode. Thus,

this change in reflected light is sensed and converted into

electrical signals for data reading purposes.

Unlike magnetic disks, which have several concentric

circles (or tracks), an optical disk has one long spiral track,

which starts at the outer edge and spirals inward to the

center. Here the track is also split up into sectors. There are

two types of optical disks: Compact Disk (CD) and Digital

Versatile Disk (DVD).

I. Compact Disk (CD):




The name Compact Disk is due to that a large

amount of data is stored in compact form in the disk.

Different versions of CDs are available now-a-days

such as CD-ROM, CD-R, CD-RW.

CD-ROM: These disks are pre-recorded i.e. data

have been written at the time of manufacture, which cannot

be altered. These disks are shiny, silver color metal disks

and generally the capacity of the disk is of 650 MB or 700MB and diameter is 5¼ inch (or 12 cm.).

CD-R: It stands for CD- Recordable disk and

popularly called as WORM (Write Once Read Many) disk.

These CDs are purchased blank and contents written by the

user only once and read the data as many times as desired.

Multiple sessions is allowed now-a-days to these disks

while writing data. A 12 cm disk can hold 650/700 MBand an 8 cm disk can hold 184/300 MB of data.

CD-RW: It stands for CD- Read and Write disk.

These types of CDs can be written as many times as

required by erasing the previous data and also read as

many times as required. Multiple sessions also allowed in

these disks while writing data. A 12 cm disk can hold

650/700 MB and an 8 cm disk can hold 184/300 MB of data.




II. Digital Versatile Disk (DVD):

This can store a huge amount of data

compared to CDs. This is achieved by making the pits

smaller and the spiral track tighter. In DVDs, laser

beam of shorter length is used and data can be written

on one or two layers of a surface. It is so named because it can store verities of programs, application in

digital form. The data storage capacities are 4.7 GB,

8.5 GB, 17 GB and 20 GB for two different sizes of

DVDs (12 cm and 8 cm). Different versions of DVDs

are available now-a-days such as DVD-ROM, DVD-R,

DVD-RW.

DVD-ROM:

These disks are pre-recorded i.e. data have

been written at the time of manufacture, which cannot

be altered. These disks are shiny, silver color metal

disks and generally the capacity of the disk is of 4.7

GB or 8.5 GB and diameter is 5¼ inch (or 12 cm.).

DVD-R:




It stands for DVD- Recordable disk and also a

WORM disk. These DVDs are purchased blank and

contents written by the user only once and read the

data as many times as desired. Multiple sessions is

allowed now-a-days to these disks while writing data.A 12 cm disk can hold 4.7/8.5 GB of data.

DVD-RW:

It stands for DVD- Read and Write disk. Thesetypes of DVDs can be written as many times as

required by erasing the previous data and also read as

many times as required. Multiple sessions also

allowed in these disks while writing data. A 12 cm

disk can hold 4.7/8.5 GB of data.




MICROPROCESSOR

When the Arithmetic and Logic Unit (ALU) and Control Unit

(CU) are merged on a single silicon chip, it is known as a

microprocessor.

With the advances in LSI and VLSI technology it became possible to build the whole CPU of a digital computer on a

single IC chip. A CPU built on a single LSI or VLSI chip is

called a microprocessor.

The microprocessor operates on binary digits, 0 and 1,

also known as bits. These two digits are represented in terms

of electrical voltages in the machine. Generally, 0 representsone voltage level and 1 represents another. The digits 0 and 1

are synonymous with low and high respectively. Each

microprocessor recognizes and process a group of bits called

the word, and microprocessors are classified according to their

word length. For example, a processor with an 8-bit word is

known as an 8-bit microprocessor , and a processor with a 16-

bit word is known as a 16-bit microprocessor , and a processor with n-bit word is known as an n-bit microprocessor (where

n=4, 8, 16, 32, 64, 128 etc.). When a microprocessor is used in

side a computer, it is known as micro computer. Today’s

computers are also of these micro computers.




Different companies like Intel, Motorola, AMD, Zilog,

Hitachi, Silicon Graphics, Cyrix, Sun etc. are manufacturing

different types of microprocessors.

INTEL Microprocessor Family:

The Intel Corporation was founded in the year 1968. Intel

believes in innovations. Its innovative principle led it to create

very effective, fastest and popular microprocessors whichleave other companies behind.

Intel Corporation introduced the first 4-bit

microprocessor, Intel 4004 in 1971 which was primarily used

in calculators.

Then it introduced the first 8-bit microprocessor, Intel 8008 in

1972. Then Intel 8080 (8-bit) microprocessor was introducedin 1973, which became the brain of first Personal Computer

(PC) - the Altair. Then Intel 8085, 8-bit microprocessor (in

1975) was manufactured with software compatible form.

Then the 16-bit microprocessors were developed. Intel

8086 (in 1978) which perform all arithmetic operations in

binary, Intel 8087 (in 1979) which perform numeric data, Intel 8088 (in 1980) which is cheaper and used in PC/XT (Personal

Computer with Extended Technology) was manufactured.

Then Intel 80186 (in 1981) with smaller number of IC’s which

made the computer compacted, Intel 10188 (in 1981) which




was designed for low cost embedded control application. Then

Intel 10286 (in 1982) which was compact in nature, inbuilt

software. So widely used in PC/AT (Personal Computer with

Advanced Technology).

Then the 32-bit microprocessors were manufactured. Intel

80386 (in 1985) was introduced with having multi-user

multitasking feature, software protection and a large memory

system. Intel 80486 (in 1989) was introduced having same

features of 80386 and with an extra feature i.e. cache memory

inbuilt with the chip for faster execution.

Then the 32-bit microprocessors with superscalar

architecture were manufactured. A microprocessor

architecture which having more than one execution unit is

known as superscalar microprocessor architecture.

I. Intel Pentium (in 1993) was introduced withimprovement to the architecture, software upward

compatible etc. It is also a 32-bit microprocessor.

The Pentium microprocessor was organized with

three execution units i.e. it is possible to execute

three instructions simultaneously.

II. Intel Pentium Pro (in 1995), a 32-bitmicroprocessor was introduced with advancement

over Pentium. It executes five instructions

simultaneously.




III. Intel Pentium II (in 1997), a 32-bit

microprocessor was introduced with MMX (Multi

Media eXtension) technology which interacts

with the data in form of text, graphics, images andsound also.

IV. Intel Celeron (in 1999), a 32-bit microprocessor

was introduced with Pentium Pro technology but

with specific market segments with a low price

and widely used for commercial purposes.

V. Intel Pentium III (in 1999), a 32-bit

microprocessor was introduced with the features

of Pentium II and with advanced imaging, 3-D

simulation, video and audio streaming and speech

recognition facility to boost the multimedia performance.

VI. Intel Pentium 4 (in 2000), a 32-bit

microprocessor came with all previous features

and having to create professional quality movies,

deliver TV like video via the internet,

communicate with real time video and voice,render 3-D graphics in real time, quickly encode

music for MP3 players and much more. It is much

smaller and faster compared to others because




physically small transistors are used in a large

amount to make this chip.

VII. Intel Xeon (in 2001), a 32-bit microprocessor popularly used in workstations and servers with

high performance. The Xeon processors

commonly used for server side applications.

VIII.

Intel Itanium (in 2001), a 64-bit microprocessor was introduced with ten instruction units to

execute simultaneously. The processor delivers

world class performance for the most demanding

enterprise and high performance applications,

including e-Commerce, security transactions,

large databases, computer aided designing and

sophisticated scientific and engineeringcomputing.

IX. Intel Pentium M (Mobile) (in 2003), a 64-bit

microprocessor is used in mobile computers with

a new technology called Centrino mobile

technology. This technology has built-in wirelessLAN (Local Area Network) and extended battery

life facility.




MOTOROLA Microprocessor Family:

The Motorola Company was founded in the year 1930. Itis the manufacture of several products in the field of

automotive, broadband technology, embedded computer

products, phones (land and mobile), energy systems, radios,

semiconductors etc.

Motorola Company introduced the first 8-bit

microprocessor, MC 6800 in 1974. It was followed by

advanced microprocessors of 8-bit are MC6802, MC6809.

In 1979, Motorola introduced an advanced powerful 16-

bit microprocessor MC68000. Then followed by it Motorolaintroduced MC68008 (in 1982) and MC68010 (in 1983) which

are 16-bit microprocessors. Then in 1984, an advanced 32-bit

microprocessor MC68020 was introduced by Motorola. In

1987 MC68030, a 32-bit microprocessor came with MMX

technology. In 1989, Motorola introduced MC68040, a 32-bit

microprocessor with some coprocessors. In 1995 MC68060, a

32-bit microprocessor launched by Motorola with softwarecompatible facility and with a memory management unit for

high performance.




AMD (Advanced Micro Devices) Microprocessor Family:

The AMD was founded in 1969. It is a competitor of Intel

Corporation. It produces microprocessors, memory devices

and silicon chips for communication and networking

applications.

AMD manufactured so many microprocessors of 32-bit.

Some of them are Nx586, Am486, Am5x86, K5, K6, K6-MMX,

K6-2, K6-3 and K7. K5 was an alternative to the Pentium. K6

was an competitor of Pentium-II and used in mobile

computers. Then AMD Duron, AMD Athlon of 32-bit was

introduced in the market.

Then AMD launched the 64-bit microprocessors. AMD

Opteron, AMD Athlon 64 are of two categories of this

microprocessor.

APPLICATIONS OF COMPUTERS




Today, computers are used in varieties of

applications. It is used in every step/walk of life. So, it isvery difficult to list out all the applications of computers.

However, some popular applications of computer are

given below:

1. Office automation (maintain records, databases etc.)

2. Electronic mailing (E-Mail)

3. Industries (Payroll, Personal information, Meetings

etc.)

4. Libraries (Book records, Renewal, Overdue etc.)

5. Reservations (Transport, Railway, Airway etc.)6. Educations (School, College, University etc.)

7. Hospitals (X-Ray, ICU, Scanning etc.)

8. Banks (Financial transactions)

9. Traffic controls (Traffic light control)

10. Crimes (Record of crime, criminals, cops etc.)

11. Multimedia (Movies, Animations, Presentations etc.)

12. Defenses (Launching missiles, Encryption,Decryption etc.)

13. Researches (Satellite communication, Testing

weapons etc.)

14. Meteorology (Weather Forecasting)




15. Entertainments (Video Games)

16. Retail Stores (Maintain bills, Stocks, Prices etc.)

POWER SUPPLIES

Since computer is an electronic device, it also

requires electric power to run. Each computer has an in-builtSMPS (Switch Mode Power Supply) to gain electricity.

Normally 230 Volt AC power (Home Current Available) is

supplied to the SMPS. It converts this power supply to a

suitable form of the computer, so that the computer runs

smoothly. For providing correct power supplies to the

computer following equipments are used:

a. CVT:




It stands for Constant Voltage Transformer.

When the input voltage fluctuates, there is a chance of

damage of circuits; at that time to supply a constant

output voltage to the SMPS of computer it is used.

b. UPS:

It stands for Uninterrupted Power Supply.When we are working in a computer, the programs are

normally loaded in the RAM. Since we know RAM is a

volatile/temporary memory, so it can be lost if power

failure occurs; unless we save the programs in any non-

volatile/ permanent memory. This problem can be

avoided by using an UPS. Even when the power failure

occurs, the UPS supplies power to the computer for ashort time period. So that we can save the data and

safely turn off the computer. UPS with different backup

power supply time are available. Its minimum backup

time is 15 minutes.

The CVT only supply constant power source but not backup power but the UPS serve as a CVT with backup

power supply.




INPUT UNIT AND OUTPUT UNIT

A computer system can be useful, only when it is able to

communicate with its external environment or with its users.To provide the means of communication between the

computer and the real world, the units available are called as

input and output units (I/O units).

To feed data and instructions from the outer world to the

computer, a unit is available called as input unit. The devices

used to do this job are called as input devices.

To receive data and instructions from the computer and provide them to the outer world, a unit is available called as

output unit. The devices used to do this job are called as

output devices.

The input and output devices (I/O devices), together

called as peripherals of a computer system.

INPUT DEVICES:

Data and instructions are entered into a

computer through input devices. An input device converts




input data and instructions into suitable binary form which can

be accepted by the computer and store them in main memory.

The input devices are broadly classified into the following

categories:

Typing devices

Pointing devices

Scanning devices etc.

Some of the commonly used input devices are discussed

below:

Keyboard:

It is one of the most commonly used input devices.

Keyboard is very much similar to a standard typewriter’s

keyboard with a few additional keys. The additional keys are

used to perform special functions such as loading a program,

editing, and deleting. Keyboard allows data entry into a

computer system by pressing a set of keys, so it is a typinginput device.

When a key is pressed from the keyboard, an electronic

pulse is generated, which is encoded and give the binary value

of the key which is pressed.

Today, in a standard keyboard, there are 104-keys

available and it is known as QWERTY keyboard . Alsodifferent types of keys are available such as:

Numeric Keys: 0 to 9 and operator keys (such as +,

–, *, / etc.)

Alphabetic keys: A to Z

Function keys: F1 to F12




Special keys: Ctrl, Alt, Insert, Delete, Home, End,

Shift, Tab, Enter, Backspace etc.

Cursor movement keys: up, down, left and right arrow

keys.

Mouse: It is also one of the most commonly used input

devices. This device is named as mouse because of its shape.

It is a small hand-held device, which can comfortably fit in a

user’s palm. The cursor on the screen can be controlled by the

movement of the mouse. The mouse can be used for quick

positioning of the cursor on the desired menu item or an icon.The mouse has 2 or 3 or 5 buttons available at the top to do

the above jobs. By pressing the buttons, we can select or open

or execute an menu. Earlier days, the mouse is rolled on a flat

pad called as mouse pad . Now different types of mouse are

available such as ball mouse, optical mouse and cordless

mouse.

SCANNERS: Scanners are basically input devices that

are capable of recognizing marks or characters. Thus they

are used for direct entry into the computer system. The

following are the characteristics of the scanners:

• Eliminate duplication of

human effort.

• Data accuracy.

• Demand high quality of

input documents.




• Form designs and inks

specifications become more critical.

• Not economically

feasible.

** Scanners are of 2 types Optical scanners and magnetic

ink character recognition devices.

.

OPTICAL SCANNERS: optical scanners are of two types

those are OMR and OCR.

OMR: The actual technique used by an OMR device for

recognition of marks involves focusing a light on the page

being scanned and detecting the reflected light pattern

from the marks. Pencil marks with a soft lead pencil will

reflect the light. These are used for evaluation purposes.

OCR: These devices are capable of detecting alphabetic

and numeric characters printed on paper. These characters

may be either typewritten or hand written. The actual

technique used by an OCR device is examines each

character as if it were made up of a collection of minute

spots. Once the whole character has been scanned, it is

compared with the characters the machine has been

programmed to recognize. Whichever pattern it matches,

or nearly matches, is considered to be the character read. If

the scanned character does not match satisfactorily with

any fonts it is rejected.




MAGNETIC-INK CHARACTER RECOGNITION:

These devices are developed to assist the banking industryin processing the tremendous volume of checks being

written every day. A special type of cheque is used in

banks that employ MICR devices. The bank’s

identification code and the customer’s account number is

pre-printed on all these cheques with a special ink that

contains magnetizeable particles of iron oxide. Evenroughly handled, folded, smeared and over stamped

cheques can still be read with a high degree of accuracy.

OUTPUT DEVICES:

Output devices are those, which links the computer

with the external environment. The processed results are

produced to the external environment by these output




interfaces. Some of the most commonly used output

devices are:

1. Monitor/VDU.

2. Printers.3. Plotters

MONITOR/VDU:

A typewriter like keyboard, is used to

enter data into the computer, and a cathode ray tube (CRT)

that looks like a television screen is used to display the

input data as well as the messages and processed output

from the computer. The terminal consists of a smallmemory known as a buffer. The size of this buffer is

normally equal to the total number of characters usually 24

rows X 80 columns that can be displayed at a time on the

terminal screen. Each character entered through the

keyboard is stored in the buffer and its displayed

simultaneously on the CRT.

PRINTERS:




Printers are the most common o/p devices in a computer

system. They are the primary output devices used to

prepare permanent documents in human-readable form(hard copy). There are several types of printers that are

designed for different types of applications. Depending on

their speed and approach of printing. Printers are classified

as character printers, line printers, and page printers.




A. Character printers: Character printers print only on

character at a time. A typewriter is an example of character printers. These are classified as impact and non-impact

printers.

1. Impact Printer: Use of Electro-mechanical mechanism

that causes hammer or pins to strike against a ribbon on a paper to print the text.

Examples of impact printers are –

a) Dot matrix printer

b) Daisy wheel printer

1.1 Dot-matrix Printers:

• These printers print each character as a

pattern of dots.

• The print head comprises a matrix of tiny

needles, typically seven rows with 9 needles in each.

• These printers’ prints in the range of 40

to 250 characters per second.

• These do not have a fixed character font.

• These can able to print graphics such as

charts and graphs.




1.2 Daisy wheel printers:

• These are also known as letter quality printers.

• These printers use a printwheel font known as a

daisy wheel.

• Each petal of the daisy wheel has a character

embossed on it.

• The desired character spins to the correct position,

a print hammer strikes it to produce the output.• This ranges from 10 to 50 characters per second.

2. Non – Impact printers: Use of laser beam or inkjet

technology for printing the text.

Examples of Non – Impact printers:

a) Inkjet Printer

b) Laser Printer

2.1 Inkjet printers:

1. They print characters by spraying small drops

of ink onto paper.




2. Special type of ink having a high iron content

is used.

3. Droplets of ink are electrically charged after

leaving a nozzle.

4. Produces high quality output.5. They can print multiple character styles and a

variety of type sizes.

6. They cannot produce multiple copies of a

document in a single printing.

2.2 Laser printers:

1. They use laser or light source to produce an

image on a photosensitive drum.

2. They produce high quality output.

3. These are quite expensive.4. They can produce 10 pages per minute. But

they produce one page at a time.




B. Line printers: A line printer is a printer that prints one

line at a time. These produce low quality output, basically

used in organizations for large volume of data.

There are 2 types of line printers a) Drum printer and b) chain

printer

Drum printers:

Consists of a cylindrical drum that has raised characters in

bands on its surface.

a. Striking a hammer against its embossedcharacter prints a character.

b.All characters on the line are not printed at

exactly the same time.

c. Speed of drum printers is in the range of 300

to 2000 lines per minute.

Chain printers:

a. They use rapidly moving chain called a print

chain. Each link of the chain is a character

font.




b. As the print chain rotates the properly timed

print hammers strike the paper, along with

the inked ribbon, against the proper

character on the chain/band as it passes.

c. Speeds of printers range from 400 to 2500characters per minute.

PLOTTERS:

A plotter is an output device used to produce hard copies of

graphs and designs. Plotters are basically of two types – drum

and flatbed.

Drum plotter:

1. The paper on which the design has to be made is placed over a drum.

2. Drum rotates back and forth to produce vertical

motion.

3. One or more penholders mounted horizontally

across the drum so that they can move to produce

horizontal motion.

4. They can also produce multi colored designs.

Flatbed plotter:

1. Consists of a flatbed of a rectangular shape.




2. The pen-holding mechanism is designed to

provide all the motion.

3. These can be used in the design of cars, ships,

aircraft’s, buildings, Highways, etc.

THE END

By Manoranjan Dash













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