Input and output units

Input and output devices are usually called peripherals. Peripheral devices can be classified according to their functions: input, output and storage devices.

A storage device is a device that is used to store the information such as hard disk drive, flash drive, floppy disk, tape drive or compact disk.

The part of the computer that takes in information is called the input unit. The input unit or device provides the means of communication between the computer and the people who are interested in its operation.

To be accepted by the machine, information for a digital computer has to be in the for of digits 0, 1, 2, 3, 4, …9 or characters A, B, C, D, … . The characters are regularly expressed for the computer's purposes as six or seven 1’s and 0’s. The 1’s and 0’s may be expressed for the computer as punched holes (1) and blanks (0) in a card or a paper tape; as presence (1) and absence (0) of electrical pulse; or as polarized spots on a magnetic surface; for example, south-north is 1 and north-south is 0, or vice versa, etc.

So, the input unit makes possible communication from the other data-handling equipment and human being to the computer. It is the functional part of the computer that accepts the data to be operated on and programs for operating. It may consist of a keyboard operated tape – punch, a paper tape reader, a card reader, and an electric typewriter. The examples of common input units are keyboards, mice and scanners.

The part of a computer that puts out information is called the output unit. The computer can easily put out information in a form acceptable to human beings. For example, the computer may give impulses to an electrical typewriter, so that the keys are energized in the proper sequence of type out a message in ordinary typed characters which human beings can read, etc.

The output of a computer is known to vary according to the capacity of the auxiliary equipment receiving the information. A computer can record on a magnetic tape at the rate of 1,000,000 characters per second. It can also control: a paper tape punch which will punch a paper tape at the rate of 100 characters per second; or a card punch which will punch per second about 300 standard punch cards of 80 columns; or a high-speed line-printer which will punch 20 lines per second, each of 80 to 120 characters. The output unit of a computer can be represented by monitors, printers and speakers.

Peripherals are directly connected to an electronic module inside the system unit called a device controller. For example, the speakers of a multimedia computer system are directly connected to a device controller called an audio card (such as SoundBlaster) which in turn is connected to the rest of the system.

All this peripheral equipment is slow as compared with, the computer. Consequently, for efficient use of the computer's tremendous calculating speed, devices called buffers may be used. A buffer is known to be a storage device which is able to take in information at a very high speed from the computer and release the information at the proper speed for the peripheral equipment.

A human being is known to write by hand at the rate of about 30 words per minute, or to type at the rate of about 60 words per minute, or to talk at the rate of 200 or 250 words per minute. The ratio between a computer speed of about 40,000 words per second, and the top output speed of a human being of about 4 words per second, gives a factor of advantage to the computer of about 10,000 to 1 at the beginning of the 60’s. Nowadays this ratio is much more.