Operating systems are ana essential part of any computer system.An operating system acts as an intermediary between the user of a acomputer and the computer hardware.The purpose of an operatig system is to provide an environment in which a user can execute programs in a convenient and efficient manner.

An operating system is software that manages the computer hardware as well as providing an environment for application programs to run .To best utilize the CPU,modern operating system employ multiprogramming,which allows several jobs to be in memory at the same time,thus ensyring the CPU always has a job to execute.

A process is the fundamental unit of work in an operating system.Operating system manages memory by keeping track of what parts of memory are being used and by whom.The operating system is also responsibile for dynamically allocating and freeing memory space.

Operating system provide a number  of services.At the lowest level,system calls allow a running program to make requests from the operating system directly.At a higher level, the command interpreter or shell provides a mechanism for a user to issue arequest without writing a program.System services can be classified into several categories:program control,status requests,and I/O request.

The design of a  new operating system is a major task.It is important that the goals of system be well defined before the design begins.

Since an operating system is large,modularity is important.Designing a system as a squence of layers of using a microkernel is considered a good technique.

Operating systems are now almost always written in a systems-implementation language or in a higher-level language.This feature improves their implementation,maintenance,and portability.To create an operating system for a particular machine configuration ,we must perform system generation.