Operating-System Services

The OS provides certain services to programs and to the users of those programs.

1. Program execution: The system must be able to load a program into memory and to run that program. The program must be able to end its execution, either normally or abnormally (indicating an error).

2. I/O operations: A running program may require I/O. This I/O may involve a file or an I/O device.

3. File-system manipulation: The program needs to read, write, create, delete files.

4. Communications : In many circumstances, one process needs to exchange information with another process. Such communication can occur in two major ways. The first takes place between processes that are executing

on the same computer; the second takes place between processes that are executing on different computer systems that are tied together by a computer network.

5. Error detection: The operating system constantly needs to be aware of possible errors. Errors may occur in the CPU and memory hardware (such as a memory error or a power failure), in I/O devices (such as a parity error on tape, a connection failure on a network, or lack of paper in the printer), and in the user program (such as an arithmetic overflow, an attempt to access an illegal memory location, or a too-great use of CPU time). For each type of error, the operating system should take the appropriate action to ensure correct and consistent computing.

6. Resource allocation: Different types of resources are managed by the Os.When there are multiple users or multiple jobs running at the same time, resources must be allocated to each of them.

7. Accounting: We want to keep track of which users use how many and which kinds of computer resources. This record keeping may be used for accounting or simply for accumulating usage statistics.

8. Protection: The owners of information stored in a multiuser computer system may want to control the use of that information. Security of the system is also important.