What is an operating system?

The interaction between hardware and software which is managed by a program is called operating system. Examples: DOS, LINUX, UNIX, etc. It allows user to format disks, print, copy, delete, display, files, control input and output operations etc.

The portion of operating system which is always present in the memory is called kernel or nucleolus. The kernel is a master program of OS. It coordinates all other parts of OS.

Main Functions of the operating system:

Memory management:

The fundamental duty of an operating system is to manage memory available to it and its applications. When the user requests that a program be run, the operating system determines the amount of memory required for the program instructions and for data, the OS allocates the amount of memory required and loads the program into RAM. When the program terminates, its memory space is declared free and same memory are allocated to another program.

Backing store management:

The operating system controls the transfer of data from secondary storage (i.e. disks) to memory and back again. It also has to maintain directory of the disk so that files and free space can be quickly located.

Interrupt handling:

THE operating system deals with many different kinds of interrupt such as for example a user pressing the enter key on the keyboard, a printer sending a message that is out of paper, the real time clock interrupting to indicate that processor should be allocated to the text user in multi-user system, a hardware software malfunction.

Resource allocation and scheduling:

In a larger computer system which is capable of running several programs at once, the operating system is responsible for allocating processing time, memory and input-output resources to each one. While the program is executing, the operating system is scheduling the use of input and output devices for other jobs. Not all jobs are performed in order they are submitted. The operating system schedules them in order to make the best possible use of computers resources.

There are many other functions of operating system they are listed below: 

a) The scheduling and landing of programs in order to provide continuous sequence of processing or to provide appropriate response to events.

b) Control over hardware resources, e.g. control over the selection and operation of devices used for input, output or storage.

c) Protecting hardware, software and data from improper use.

d) Calling into main storage programs and subroutines as and when required.

e) Passing of control from one job (Program) to another under a system of priority when more than one application program occupies main storage.

f) Provision of error correction routines.

g) Furnishing a complete record of all that happens during processing (usually in the form of a printed log).

h) Saving the contents of files to a disk for permanent storage, and reading the contents of files from disk into memory.

i) Some O/S provides a feature called virtual storage; with which it is possible to increase the capacity of main memory without actually increasing its size.

j) Allocating RAM for various programs.

k) It provides users an interface to computing resources. It processes user's commands.

l) In a multi-user system it allows several users to share CPU on the time share basis; to share other system resources; it performs job scheduling; prevents interference between different users between users and operating system; provides memory management etc.

m) It monitors execution of user programs.

n) Maintaining an orderly system files on disks. 

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