Anatomy of Computer-Input Device

          In principle, a computer of any kind works in much the same way as a teacher. It is concerned with accepting data as input, storing all the information, which is relevant to it, processing the data in a pre-determined way that confirms with a program of instructions and then communicating the results as output. Thus a computer essentially consists of three elements.

1.        Input Device
2.       Central Processing Unit CPU
3.       Out Device

Input and output devices provide, man to machine and machine to man communication and since, they surround CPU, and they are also called peripheral devices.

Input Devices:

Input devices are of many types but basically they are meant for presenting the information of computer in machine readable form. A computer system may have one or more of following input device depending upon its type, size and use.

1.        Punch Card Reader
2.        Punched Paper Tape Reader
3.        Magnetic Tape
4.        Magnetic Disk
5.        Floppy Disk
6.        Teleprocessing Terminal Teletype Writer Terminal
7.        Optical Scanner
(a) Optical Mark Reader;
(b) Optical Character Reader (OCR)
8.        Magnetic Ink Character Reader (M.I.C.R.)
9.        Visual Display Unit (VDU)
10.      Voice Data Entry Terminal (V.D.E.)

Mouse System
Digitizer Graphics Tablet
Optical Bar Reader

Types of Digital Computers

Classification based on memory size: digital computers are also classified in accordance with their memory size as below:

1.        Micro Computers
2.       Mini Computers
3.       Mainframe Computers
4.       Super Computers

Digital Computer

Micro Computers:

A micro computer is called micro for two reasons. One because it is miniature in size and another because it uses micro processor. Micro processor is actually the heart cum mine of a computer. The entire CPU of a microcomputer is contained either in a single chip of thumbnail size, or on a few chips. When equipped with memory and input/output control circuitry he micro processor is known as micro computer. Early micros had a word length of 8 bits but currently 16 bit micros are available at work to develop 16 bit micros. The speed of micro computer is of the order of 100 kips. Micro computers have generally a visual display unit, keyboard, one or two floppy disk drives and printer and may be interfaced with some tools like digitizer, joy stick, tracker ball, light pen, etc. they have memory range of 16 to 512 kilobytes. Mini Winchester disk drive may be attached with a capacity of 10 MB if needed.

Mini Computers:  

The computer designed to be used by a small group 4 to 6 simultaneously is known as a mini computer multi user. Mini computers are at least five times faster than micro computers having CPU speed of approximate 500 kilo instructions per second. Such systems are characterized by their main memory size, which may be 256 KB to 12 MB and word length of 16/32 bits. They use Winchester hard disks drives of 80 MB each, 1 or 2 floppy drives, 7 to 8 printers, 9 on line printers, digitizers, plotters and fixed storage of 160 Mb and magnetic tapes.

            A slicing time sharing system is used in this type of computers where a predefined amount of time (few seconds) is allocated to each user (terminal). So, let’s there are about 6 users using the system simultaneously. Then the computer will start attending all the users one by one with a specified interval of time. Say if the time interval is 5 seconds a terminal then the first user will get his time of 5 seconds again after 30 seconds of time.

Mainframe Computers:

These are the large size computers which occupy a large air conditioned roomful space and main memory size up to 128 megabyte. Since all its peripherals are mounted in large cabinet type of frames, these computers are also known as main frame computers. 128 users can use such a computer system simultaneously in time sharing mode and employing mini computers as a front end processor. All the first to third generation mode and employing mini computers as a front end processor. All the first to third generation computers, which work with the speed of 5 to 100 million instructions per second, fall under this group. Burroughs 800 UNIVAC 1100/60, ACOS 100 is the popular main frame computers.

Super Computers:

Super computer means a computer having main memory of 256 megabytes. This computer is 5 million times faster than the first computer i.e., ENIAC. Since the very high cost of this machine, it is exclusively used in the organizations where the speed is the criteria. With less than 10 installations in India, these computers are employed in weather forecasting, defense etc.

             On the first super computer ILLIAC-IV, 64 different calculations could be made at a time, i.e., it was equivalent of 64 different mainframe computers. It was the first large scale array computer, which became operational in November 1975. Arithmetic can be performed in 8, 32 or 64 bit mode. The ILLIAC can execute instructions at a rate of 300 millions per second.

Types of Computers

A computer can be classified as one of the following depending on the type of the data it is to process.

1. Digital Computers
2. Analog Computers
3. Hybrid Computers

Digital Computers:

In digital computers, mathematical expressions are finally represented as binary digital (0 and 1) and all operations are done using these digits at very high rate. The digital computer basically knows only how to add. Remaining operations like multiplication, division and exponentiation etc., are first converted into addition and the calculated. A digital computer operates in inputs that are on off or incrementally stepped quantities which are represented by numerical digits.

Analog Computers:

Analog is a Greek word, which means establishing similarities between two quantities. In analog computer, similarities are established in form of operated by measuring rather than by counting. For example, the speed of an automobile as measured by a speedometer, or the temperatures of a patient as measured by a thermometer.

            Analog computers cannot compute directly with numbers. Rather, they deal with variables that are measured along a continuous scale and are recorded to some predetermined degree of accuracy. Temperature for example, may be measured to the nearest tenth of a degree of a Celsius scale. A petrol pump may contain an analog processor.

Hybrid Computers:

These computers will have the desirable features of digital and analog computers. For example, a patient monitoring system installed in a hospital will have to obtain the temperature of a patient analog and convert it to the nearest decimal value before displaying it in digital form.

Generation of Computers

The development of the computer right from its inceptions to today’s most sophisticated version can be classified into different stages. Catch stage with a period of about 10 years is known as a generation. Hence the first generation is during 1950 -1960 and 1960-1970 is the second generation 1970-1980 the third and 1981 and after is the fourth generation computers. Though the fifth generation computers were to start in January 1990’s the fifth generation has not been announced due to the delay in research work caused by the technical limitation.
The Following is a Brief of each Generation:

First Generation Computers:

These computers were using thousands of Vacuum tubes approximate in each computer due to which the size of the machine used to be very large and the cost used to be very high. Since the life of a vacuum tube is very small these machines could have been used only for a short time and once a tube is burnt out the machine would have stopped working until a new tube is replaced.

Since no compilers were invented by then programming in these machines were performed by physical connecting and disconnecting wires which used to take huge amount of time of skilled professional. Inspire of all these hurdles computer was a wonderful invention and people by and large have accepted and adopted this machine. Thus made today computer possible.

Second Generation Computers:

The remarkable invention of the transistor and the high level language has made these 2nd generation computers smaller farter and with greater computing capacity. Unlike the earlier computers the 2nd generation computers were designed with non scientific processing requirement in mind. The invention of transistor in 1948 led to the development of 2nd generation computers. Although faster smaller and more powerful they were still expensive machines which only large commercial organization could afford.

Third Generation Computers:

In 1964 the 3rd generation computers were introduced. These had integrated transistor circuits having higher speed larger storages capacities and lower prices. These computers were called mini computers. Instead of having one transistor of its own several transistor could be integrated with the other components and sealed up in a small package. The package was called an integrated circuit I.C. or more popularly a chip was invented by jack Kirby at Texas instruments in 1958. the manufacturing of mini computer of 3rd generation began after development of large scale integration and very large scale integration and microprocessor chips.

Fourth Generation Computers:

ICs which have the entire computer circuitry on a single silicon chip are called MICRO-PROCESSORS. The computer using chips are called micro computers or in story micros. Due to development of microprocessor chip in 1971 by Intel Corporation of U.S.A another breed of computers known as micro computers came into existence in 1974 and became popular as 4th generation of computers. The personal computer developed by the multinational giant IBM in 1984 uses 16 bit microprocessor and belongs to 4th generation of computers.

History of Computers

                Though the first Electronic general purpose computer (ENIAC) was available in early 1940’s the history of the calculating machine starts as early as 1642 during which the first mechanical calculating machine was developed by basic, Pascal, a brilliant young Frenchman. About 30 years later, Gottfried Von Leibniz, a German mathematician, improved upon Pascal’s invention by producing a calculating machine which could add subtracts, multiply, divide and improvised calculating machine, a major break through was the development of electro mechanical punched card equipment invented by Dr. Herman Hollerith, a statistician. In 1887, Hollerith developed his machine, readable card concept and designed a device known as the “CENSUS MACHINE”. In 1896 he founded the tabulating machine company to make add sell his invention. Later this firm merged with others to form what is now known as International Business Machines Corporation (IBM).

The Stone Age man used pebbles for counting cattle. Latter on when man became more civilized abacus came in use. Abacus seems to be the earliest calculating machine which was developed by Chinese 3000 years ago. Interestingly enough abacuses are still being used in Soviet Union, Japan, Far East and even in India for primary education. It consists of a rectangular wooden frame with horizontal rods. Which carry round beads? Counting is done by shifting the beads on left hand side of cross bar have a value of five and each of the five beads on right hand side of cross bar have a value of one. The topmost line represents the unit digit second line tens digit third line hundreds and so on. Numbers are entered in reverse order starting from top to bottom.

Analog Machines and Napier Bones:-

John nippier the Scottish mathematician devised a set of fords for use in calculations invoicing multiplication. These rods were carved from bones and therefore called as nappies bones.

Odometer (Speedometer) and Logarithm:-

Sometimes later odometer was discovered perhaps before the birth of Christ which led to development of mechanical adders and multipliers. In 1617 john Napier the distinguished Scottish mathematician developed the method of logarithm. Logarithmic tables represent actually analogue computing technique. N this system multiplications and divisions can be done by adding and subtracting not the numbers themselves but with the help of a related numbers known as logarithm. Logarithm is nothing but an application of indices. By use of logarithms arithmetical calculations regarding multiplications division’s square roots and factions can be easily simplified by referring to standard tables. If swore of 3 is nine then 2 is the logarithm of 9 to the base 3. normally base 10 logarithm is used in which case since square of 10 is 100 then 2 is the logarithm of 100 to the base 10. Similarly since cube of 10 is 1000 then 3 is the logarithm of 1000 to the base 10.

Blasé Pascal and his Mechanical Calculator:

The first mechanical calculating machine was made in 1642 by great French mathematician and philosopher Blasé Pascal. His machine was a simple calculator used for addition and subtraction purposes. Pascal invented the calculator at the age of 18 only to assist his father in tax calculations.

Within two years he devised a working modal which was patented in years 1645. The machine consisted of gears, wheels and dials. Each wheel had 0 segments like that of milometer or house energy meters. When one wheel completed a rotation the next wheel moved by one segment. With this calculator addition and subtraction could be performed by dialing these series of wheels bearing and number 0 to 9 around their circumference. The machine was produced in mass scale and became very popular. This machine which was larder on modified by a German Gottfried Leibnitz in 1671 was the first machine to multiply and divide directly.

Charles Babbage:-

Charles Babbage another genius in history of computing made a machine called differential engine which could value accurately algebraic expressions and mathematical table correct up to 20 decimal places. Later on he was able to develop analytical machine which was an automatic computing machine designed to do assertions at the rare of 60 per minute and had memory also. His idea of using cards was derived from the work of Joseph jacquard that in France used punched cards to determine the threads to be selected in weaving partners automatically.

Computer Capabilities

Computer Performs only Three Basic Functions

1.       Arithmetic calculations i.e., Addition, Subtraction, Multiplications and Division;
2.       Compare Values
3.       Store, Search and Retrieve

It should be very clearly understood that although computer essentially does all above functions automatically, it does not possess any intelligence of its own. Its intelligence quotients or I.Q. is zero i.e. it does not have any thinking, arguing or decision-taking power of its own. This power is intelligently conferred to it by proper programming methods by persons handling it. Let us see where computer stands in comparison to human brain.

The Characteristics of a Computer:

Computers display following characteristics to a greater or lesser extent depending on their type and application. Computers are not merely calculators but are programmable calculators which help to reduce the burden on human memory and burden of mechanical processing. Computers have assumed their importance due to following capabilities.


Computers make calculations at very fast rate. But how fast? Let s multiply 383 with 186. It takes about 60 seconds for expert calculator to do this job with the help of pencil, his wisdom and memory. Similarly think how long it would take you to count up to 2 million 20 lakhs? Try! Though you are quick at counting numbers, even then it will take about a minute in counting upto 100 numbers. With this speed it will take over a week of your continuous counting. But a modern computer can do 20, 000, 000 twenty million or 2 crore such calculations in one minute and those too, without any mistake. A computer deals with that amount of arithmetic jugglery in a minute which will take entire life of a man expected to live long upto 100 years.

Super High Accuracy and Degree of Reliability:

Computers are designed in such a way that their individual components have very high life and degree of reliability. All mechanical parts have super high endurance capacity so that computer works without tiring. It works on the basis of electric pulses due to which there is no chance of its making mistakes. It can repeat the same job a number of times in exactly the same way.

Storage Capacity or Memory:

The computers have got superb inbuilt and auxiliary memory systems. A computer system can store a great amount of information in it. The success of computers lies not only in storing the information but also in the great speed of utilizing the memory storage. The computer at lightning speeds can retrieve any item of data or any instruction stored in memory. Modern computer can call back any data out of its stored memory in few nanoseconds. 1 nanosecond is 1 million times smaller than 1000th part of second i.e. 1 nanosecond= 0.000000001 second. The idea of computer having memory was encapsulated by the great scientist john von- Neumann in 1946 who was working on an atomic bomb project.


It is the ability to take in and store a sequence of instruction for obeying. Such a sequence of instructions is called a program and must be written in the languages of computer. It is also the ability to obey a sequence of program instructions, provided the instructions are stored within the computer. The program instructions will be obeyed in sequence automatically, without the need for manual intervention at each step. This very different from the operation of a typical pocket calculator which needs buttons to be pressed for each operation and where the person using the calculator controls the sequence of operations.


The ability to communicate with other systems and adopt several modern like audio, visual, user’s friendly etc.