Notes and Study Materials



The computer is an advanced electronic device that takes raw data as input from the user and processes these data under the control of the set of instructions (called program) and gives the result (output) and saves output for the future use. It can process both numerical and non-numerical (arithmetic and logical) calculations.

Characteristics of computers

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Different Generations of computers:

The development of computers has followed different steps in the terminology used and these steps of technological differences are called as GENERATIONS in computer terminology. There are totally five generations of computers till today.

I. First Generation Computers (1950's)

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Primary Memory:



There are two kinds of computer memory: primary and secondary. Primary memory is accessible directly by the processing unit. RAM is an example of primary memory. As soon as the computer is switched off the contents of the primary memory is lost. You can store and retrieve data much faster with primary memory compared to secondary memory. Primary memory is more expensive than secondary memory.


Because of this the size of primary memory is less than that of secondary memory. Computer memory is used to store two things: i) instructions to execute a program and ii) data. When the computer is doing any job, the data that have to be processed are stored in the primary memory.

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Secondary Memory:



The operating speed of primary memory or main memory should be as fast as possible to cope up with the CPU speed. These high-speed storage devices are very expensive and hence the cost per bit of storage is also very high. Again the storage capacity of the main memory is also very limited. Often it is necessary to store hundreds of millions of bytes of data for the CPU to process. Therefore additional memory is required in all the computer systems. This memory is called auxiliary memory or secondary storage.

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A computer is only useful when it is able to communicate with the external environment. When you work with the computer you feed your data and instructions through some devices to the computer. These devices are called Input devices. Similarly, computer after processing gives output through other devices called output devices.

I. Input Devices


Input devices are necessary to convert our information or data into a form which can be understood by the computer. A good input device should provide timely, accurate and useful data to the main memory of the computer for processing followings are the most useful input devices.


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