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.
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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”.
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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.
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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
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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:
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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
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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:
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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
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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
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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
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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-
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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
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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
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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
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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
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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.
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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
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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.
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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.
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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.
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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.
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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
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InputUnit
Arithmetic & Logic Unit
Control Unit
Memory Unit Output
Unit
Central Processing Unit(CPU)
Fig: Block Diagram of a Computer
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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)
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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.
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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:
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Arithmeticand
Logic Unit
(Resistors)
Cache
Memory PrimaryMemory Secondary
Memory
Fig: Memory hierarchy in a computer system
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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.
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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.
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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
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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
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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
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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:
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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:
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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.
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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
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* 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.
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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:
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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
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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
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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.
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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:
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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
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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
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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):
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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.
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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:
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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.
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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.
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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
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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.
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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
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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.
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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.
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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
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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)
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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:
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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.
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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
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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
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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.
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• 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.
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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
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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:
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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.
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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.
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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.
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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.
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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.
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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.
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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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