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Types of Services

  • An Operating system provides an environment for the execution of programs.
  • It provides certain services to programs and to the users of those programs.
  • The specific services provided are different from one operating system to another, but we can identify common classes.
  • They are as follows
    • Program execution
    • I/O operation
    • File system manipulation
    • Communications
    • Error detection
    • Resource allocation
    • Accounting
    • Protection

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

I/ O operation (Input / Output operation)

  • A running program may require I/O.
  • This I/O may involve a file or an input output 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.
  • Obviously programs need to read and write files
  • Programs also need to create and delete files by name.


  • 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.
  • Communications may be implemented via shared memory, or by the technique of message passing in which packets of information are moved between processes by the operating system.

Error Detection

  • The operating system constantly needs to be aware of possible errors.

  • Errors may occur in the CPU and memory hardware in I /O devices and in the user program.

  • For each type of error, the operating system should take the appropriate action to ensure correct and consistent computing.

Resource Allocation

  • When multiple users are logged on the system or multiple jobs are running at the same time, resources must be allocated to each of them.

  • Many different types of resources are managed by the operating system.

  • Some may have special allocation code, whereas others may have much more general request and release code.

  • This tasks aims at proper use of resources available.


  • This feature keeps 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.

  • Usage statistics may be a valuable tool for researchers who wish to reconfigure the system to improve computing services.


  • The owners of information stored in a multi-user computer system may want to control use of that information.

  • When several disjointed processes execute concurrently, it should not be possible for one process to interfere with the others, or with the operating system itself.

  • Such process is performed by giving authentication to the user, by providing user name and password.

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