An operating System (OS) is an intermediary between users and computer hardware. It provides users an environment in which a user can executeprograms conveniently and efficiently.In technical terms, It is a software which manages hardware. An operating System controls the allocation of resources and services such as memory,processors, devices and information.DefinitionAn operating system is a program that acts as an interface between the user and the computer hardware and controls the execution of all kinds ofprograms.Following are some of important functions of an operating System.Memory ManagementProcessor ManagementDevice ManagementFile ManagementSecurityControl over system performanceJob accountingError detecting aidsCoordination between other software and usersTypes of Operating SystemOperating systems are there from the very first computer generation. Operating systems keep evolving over the period of time. Following are few of theimportant types of operating system which are most commonly used.
Batch operating systemThe users of batch operating system do not interact with the computer directly. Each user prepares his job on an off-line device like punch cards andsubmits it to the computer operator. To speed up processing, jobs with similar needs are batched together and run as a group. Thus, the programmersleft their programs with the operator. The operator then sorts programs into batches with similar requirements.The problems with Batch Systems are following.Lack of interaction between the user and job.CPU is often idle, because the speeds of the mechanical I/O devices is slower than CPU.Difficult to provide the desired priority.Time-sharing operating systemsTime sharing is a technique which enables many people, located at various terminals, to use a particular computer system at the same time. Time-sharing or multitasking is a logical extension of multiprogramming. Processor's time which is shared among multiple users simultaneously is termed astime-sharing. The main difference between Multiprogrammed Batch Systems and Time-Sharing Systems is that in case of Multiprogrammed batchsystems, objective is to maximize processor use, whereas in Time-Sharing Systems objective is to minimize response time.Multiple jobs are executed by the CPU by switching between them, but the switches occur so frequently. Thus, the user can receives an immediateresponse. For example, in a transaction processing, processor execute each user program in a short burst or quantum of computation. That is if nusers are present, each user can get time quantum. When the user submits the command, the response time is in few seconds at most.Distributed operating SystemDistributed systems use multiple central processors to serve multiple real time application and multiple users. Data processing jobs are distributedamong the processors accordingly to which one can perform each job most efficiently.