Operating System

Operating system is the most important part of every computer system. It is collection of system programs that controls the operation of a computer system. It acts as an interface between a user and the computer hardware. The prime objective of the operating system is to manage and control the various hardware resources of a computer system. These hardware resources include processor, memory, disk space, etc. The another objective is to provide an interactive interface to the user and interpret commands so that the user can communicate with the hardware.

Functions of the operating system

The main functions of the operating system are as follows:

a) It handles allocation and de-allocation of memory space as required by various programs.

b) It manages files on a disk. It permits the users to create, print, copy, delete, read and write to files.

c) It controls input and output devices.

d) It protects system resources and information from destruction and unauthorized use.

e) It provides the interface between the user and the hardware.

Types of operating system

The operating system has evolved successfully from the primitive days to the present digital era. Several operating systems have been developed over the years. Basically, operating system is classified into two types:

a. Single-user operating system

b. Multi-user operating system

a. Single-user operating system

An operating system that allows a single user to perform just one task at a time such as printing a document, writing a file to disk, editing a file, or downloading a file from a network server is called single-user operating system. MS-DOS is the example of single-user operating system.

b. Multi-user operating system

A multi-user operating system allows multiple users to use programs that are simultaneously running on single network server. In a multi-user operating system environment, all or most of the computing is done at the server. UNIX, Linux, Novell network are the examples of multi-user operating system.

Computer Measurement Units

Memory of storage capacity measurement

We come across different measuring units like kilogram, meter and liter and so on to measure weight, length and capacity or volumes of different commodities. Similarly, when we have to measure the capacity of computer’s memory, storage devices and length of programs, units like kilogram, meter and liter can not be used. Hence, we use the units like BIT, NIBBLE, BYTE and WORD.

BIT

BIT is an abbreviation of the words binary digit and is the smallest units of information. It is either ‘0’ or ‘1’. The raw data fed into the computer are first converted into an electrical pulses or BITs, as the computer do not recognize the general form of data like numbers (0-9), alphabets (a-z or A-Z) and special characters like punctuation marks and arithmetic signs. The 0 and 1 of the binary system corresponds to the ON and OFF of the flow of electrical in the computer’s circuits. Computer works by recognizing the presence or absence of an electrical pulses or BITs at a particular time.

NIBBLE

A NIBBLE is a string of four BITs. The earliest form of code, called ‘Binary Decimal Code (BCD)’ used a NIBBLE for every character.

For example:

Character 3 A

BCD (NIBBLE) 0011 1010

BYTE

It is the unit of measuring computers memory and size of a program. One BYTE is the string of eight binary digits (BITS). It may represent a single letter, numeral or other characters. Computer memory is expressed in terms of Bytes, Kilo bytes(KB), Mega bytes(MB), Giga bytes(GB) and Tera bytes(TB).

8 bits = 1 byte

1024 bytes = 1 kilobyte (KB)

1024 kilo bytes = 1 Mega byte (MB)

1024 mega bytes = 1 Giga byte (GB)

1024 giga bytes = 1 Tera byte (TB)

A ‘Kilo’ should mean 10³ (10×10×10) that is 1000 bytes. However, since the computer used Binary system and 2¹⁰ (i.e. 2×2×2×2×2×2×2×2×2×2) equals to 1024 bytes, which is nearly 1000 bytes. Hence, ‘Kilo’ refers to 1024 in measuring units of computer.

WORD

A computer word is defined in terms of bytes. A word may be formed by combining two or more bytes. The most common combination if of four bytes. Word-length is a length of bits that occupy one location in memory. A computer having a smaller word-length is slower that another having a larger word-length is, though the speed of both is same. Word-length is generally fixed for a computer, but some computers have a challengeable word-length i.e. they can be used in doing small or big tasks. Nowadays computers have word-length of 16, 32, 48, 64, 128 or more bits.