Operating System perform two basically unrelated functions , extending the machine and managing resources -
1. The Operating System as an Extended Machine - The function of Operating System is to present the user with the equivalent of an extended machine or virtual machine that is easier to program than the underlying hardware .
2. The Operating System as a Resource Manager - Internally an operating system acts as a manager of resources of the computer system such as processor , memory , files and I/O devices . In this role , the operating system keeps track of the status of eachresource , and decides who gets a resource , for how long , and when .
In systems that support concurrent execution of programs , the operating system resolves conflicting requests for resources in a manner that preserves system integrity , and in so doing attempts to optimize the resulting performance .
An Operating System provides an environment for the execution of programs . It provides certain services to programs and to the users of those programs . Some of the services are been discussed below -
1 ... I/O Operations - A running program may require I/O . This I/O may involve a file or an I/O device . For efficiency and protection , users control I/O devices directly. Generally , the program that requires I/O , specifies only a function the rest of the work is handled by operating system .
2 ... Works as a Resource Allocator - When multiple users are logged on the system or multiple jobs are running atthe same time , resources must be allocated to each of them . Various types of resources are managed by operating system . Some may have special allocation code , whereas others may have much more general request and release code .
3... File-system Manipulation - Programs need to read and write files . Programs also need to create and delete files by name , all managed by operating system .
4... Error Detection - The operating system constantly needs to be aware of possible errors . Errors may occur in the CPU , memory hardware , in I/O device , and in user programs . It is duty of operating system that display appropriate message whenever an error occurs and takes the suitable action for ensuring correct and consistent computing .
5... Communication - If more than one programs are running on same computer , then there are many instances , when one process needs to exchange information with another process . Thus operating system performs the process of communication through message passing .
6... Protection - Protection involves ensuring that all access to system resource is controlled . When several disjoint programs execute concurrently it should not possible for one process to interfere with the others , or with operating system . Security of the system from the outsiders is also important . Such security starts with the user having to authenticate himself to the system , usually by means of a password to be allowed access to the resources .
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