1. Introduction to Computers
By Dalbir Singh
Computer Science Deptt.

2. Define the term computer?
A computer is an electronic machine, operating under the control of instructions stored in its own memory, that can accept data, manipulate the data (processes data) according to specified rules, produce results, and store the results for future use. Computers process data to create information. Data is a collection of raw unprocessed facts, figures, and symbols. Information is data that is organized, meaningful, and useful. A Computer can perform activities that involve Mathematical, logical and graphical manipulations. Generally, the term is used to describe a collection of devices that function together as a system

4. Characteristics of a Computer

5. Basic characteristics about computer are:
Speed
Accuracy
Diligence
Versatility
Power of Remembering
No IQ
No Feeling
Storage

6. Speed
As you know computer can work very fast. It takes only few seconds for calculations that we take hours to complete. You will be surprised to know that computer can perform millions (1,000,000) of instructions and even more per second.
Therefore, we determine the speed of computer in terms of microsecond (10-6 part of a second) or nanosecond (10-9 part of a second). From this you can imagine how fast your computer performs work.

7. Accuracy
The degree of accuracy of computer is very high and every calculation is performed with the same accuracy.
Computers can perform operations and process data faster but with accurate results and no errors. Results can be wrong only if incorrect data is fed to the computer or a bug may be the cause of an error

8. Diligence
A computer is free from tiredness, lack of concentration, fatigue, etc. It can work for hours without creating any error. If millions of calculations are to be performed, a computer will perform every calculation with the same accuracy. Due to this capability it overpowers human being in routine type of work.

9. Versatility
It means the capacity to perform completely different type of work. You may use your computer to prepare payroll slips. Next moment you may use it for inventory management or to prepare electric bills.
Computer is a versatile machine. They are used in various fields. They are used in Schools & Colleges, at hospitals, at government organizations and at home for entertainment & work purposes.

10. Power of Remembering
Computer has the power of storing any amount of information or data. Any information can be stored and recalled as long as you require it, for any numbers of years. It depends entirely upon you how much data you want to store in a computer and when to lose or retrieve these data. 

11. No IQ
Computer is a dumb machine and it cannot do any work without instruction from the user. It performs the instructions at tremendous speed and with accuracy. It is you to decide what you want to do and in what sequence. So a computer cannot take its own decision as you can.

12. No Feeling
It does not have feelings or emotion, taste, knowledge and experience. Thus it does not get tired even after long hours of work. It does not distinguish between users.

13. Storage
The Computer has an in-built memory where it can store a large amount of data. You can also store data in secondary storage devices such as floppies, which can be kept outside your computer and can be carried to other computers.
Storage capacity is another big characteristic of a computer. A computer can store large amount of data. This data can be used at any time and also from any location. The storage capacity of a computer is measured in Mega Byte, Gega Byte, Tera Byte.

14. We can do multitasking
In computing, multitasking is a concept of performing multiple tasks/applications (also known as processes) over a certain period of time by executing them concurrently.

15. History of computers

16. Ancient abacus – 2000 years back
Computers truly came into their own as great inventions in the last two decades of the 20th century. But their history stretches back more than 2000 years to the abacus: a simple calculator made from beads and wires, which is still used in some parts of the world today. The difference between an ancient abacus and a modern computer seems vast, but the principle—making repeated calculations more quickly than the human brain—is exactly the same.
Simple addition and subtraction were carried out rapidly and efficiently by positioning the beads appropriately.

17. Cogs and Calculators
In 1642, aged only 18, French scientist and philosopher Blaise Pascal (1623–1666) invented the first practical mechanical calculator, the Pascaline, to help his tax-collector father do his sums. The machine had a series of interlocking cogs (gear wheels with teeth around their outer edges) that could add and subtract decimal numbers.
Several decades later, in 1671, German mathematician and philosopher Gottfried Wilhelm Leibniz (1646–1716) came up with a similar but more advanced machine called Stepped Reckoner. Instead of using cogs, it had a "stepped drum" (a cylinder with teeth of increasing length around its edge), an innovation that survived in mechanical calculators for 300 hundred years. The Leibniz machine could do much more than Pascal's: as well as adding and subtracting, it could multiply, divide, and work out square roots. Another pioneering feature was the first memory store or "register."

18. Neither the abacus, nor the mechanical calculators constructed by Pascal and Leibniz really qualified as computers. A calculator is a device that makes it quicker and easier for people to do sums—but it needs a human operator. A computer, on the other hand, is a machine that can operate automatically, without any human help, by following a series of stored instructions called a program (a kind of mathematical recipe). Calculators evolved into computers when people devised ways of making entirely automatic, programmable calculators.

19. Engines of Calculation
In 1833, Professor Charles Babbage of Cambridge University, England who is considered the father of the modern digital computer, proposed a machine called analytical engine. However, he could not actually produce it because the technology of that time was not so advanced. Babbage’s analytical engine had a great significance in the history of computers because it had all the fundamental concepts if the modern digital computers.

20. Toward the end of the 19th century, other inventors were more successful in their effort to construct "engines" of calculation. American statistician Herman Hollerith (1860– 1929) built one of the world's first practical calculating machines, which he called a tabulator, to help compile census data.
It was used by the Census Bureau of USA to tabulate the American Census in His machine opened a new class of computing devices – Analog computers which used electrical voltages to represent physical quantities. They were extremely fast but not exact and dependable.

21. Mark-I (Automatic Sequence Controlled calculator) - 1937
The Mark-I computer also called the Automatic Sequence Controlled Calculator was fist fully automatic calculating machine developed in It was developed by Professor Howard Aiken of Harward University in collaboration with IBM. It was electromagnetic computer which was used to perform five basic arithmetic operations, like addition, subtraction, multiplication, division and table reference. It was huge in size and its design was very complex, but was very reliable.

22. Atanasoff – Berry Computer (1939-42)
The Atanasoff – Berry Computer ( ) was an electronic machine developed by DR John Atanasoff and his assistant Cufford Berry using certain mathematical equations. It used vacuum tubes and capacitors for internal logic and storage respectively.

23. ENIAC (Electronic, Numerical, Integrator, Analyzer and Computer)
The ENIAC (Electronic, Numerical, Integrator, Analyzer and Computer) was the first general-purpose electronic computer. It was developed in 1943 by the team of Professor led by Prof. J. Presper Eckert and Prof. John Mauchly at the Moore School of Engineering of the University of Pennsylvania, USA. IT used more a number of vacuum tubes and was housed in a big room. It could perform about 300 multiplications per second. It could store only very limited amount of information and its programs were wired on boards.