Operating System

A piece of low level software which is responsible for task scheduling, memory allocation, interfacing with peripheral hardware and security. An operating system is the platform upon which all other application programs are run.

An operating system can be classified as:multi-user: allows two or more users to run programs at the same time multitasking: allows more than one program to run concurrentlymultithreading: allows different parts of a single program to run concurrentlymultiprocessing: supports running a program on more than one CPU real time: responds to input instantly.

See also:
[Linux]  [Unix]