An operating system provides an environment for the execution of programs. It provides certain services to the programs and the users of those programs. The specific services provided differ from one operating system to another, but we can identify common classes. These operating system services are provided for the convenience of the programmer, to make the programming task easier. One set of operating system services provides functions that are helpful to the user
- User Interface: Almost all operating systems have a user User interface (UI). This interface can take several forms. One is a command-line interface (CLI), which uses text commands and a method for entering them (say, a program to allow the entering and editing of commands). Another is a batch interface, in which commands and directives to control those commands are entered into files are executed. Most commonly/ a Graphical user interface (GUI) is used. Here, The interface is a window system with pointing devices to direct I/O, choose from menus, and make selections and a keyboard to enter text. some system provides two or all three of these variations
- Program Executions: The system must be able to load a program into memory and to run that program must be able to end its executions, either normally or abnormally (indicating error).
- I/O Operations: A running may require I/O, which, may involve a file or an I/O device. For specific devices, special functions may be desired. for efficiency and protection, users usually cannot control I/O devices directly. therefore, the operating system must provide a means to do I/O.
- File-system Manipulation: The file system is of particular interest. Programs to read and write files and directions. they also need to create and delete them by name, search for a given file, and list file information. finally, some programs include permissions management to allow or deny access to files or directions based on file ownership.
- Communications: There are many circumstances in which one process needs to exchange information with another process. Such communication may occur between processes that execute on the same computer or between processes that are executing on different computer systems tied together by a computer network. communications may be implemented via "shared memory" or through "massage passing", in which packets of information are moved between processes by the operating system.
- Error Detections: The operating system needs to be constantly aware of possible errors. Errors may occur in the CPU and memory hardware, in I/O devices connecting failure on a network, or lake of paper printer and the user program. for each type of error, the operating system should take the appropriate actions to ensure correct and consistent computing Debugging facilities can greatly enhance the user's and programmer's abilities to use the system efficiently
Another set of operating system functions exists not for helping the user but rather for ensuring the efficient operations of the system itself. Systems with multiple users can gain efficiency by sharing computer resources among the user. When multiple jobs are running at the same time, the resource must be allocated to each of them.
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