Operating System Services

  • Operating systems provide an environment for execution of programs and services to programs and users

  • One set of operating-system services provides functions that are helpful to the user:

    • User interface -Almost all operating systems have a user interface (UI),Varies between Command-Line (CLI), Graphics User Interface (GUI), Batch
    • Program execution -The system must be able to load a program into memory and to run that program, end execution, either normally or abnormally (indicating error)
    • I/O operations -A running program may require I/O, which may involve a file or an I/O device
    • File-system manipulation -The file system is of particular interest. Obviously, programs need to read and write files and directories, create and delete them, search them, list file Information, permission management.
    • Communications –Processes may exchange information, on the same computer or between computers over a network
      Communications may be via shared memory or through message passing (packets moved by the OS)
    • Error detection –OS needs to be constantly aware of possible errors
      May occur in the CPU and memory hardware, in I/O devices, in user program
      For each type of error, OS should take the appropriate action to ensure correct and consistent computing
      Debugging facilities can greatly enhance the user’s and programmer’s abilities to efficiently use the system

    Another set of OS functions exists for ensuring the efficient operation of the system itself via resource sharing

    • Resource allocation -When multiple users or multiple jobs running concurrently, resources must be allocated to each of them
      Many types of resources -Some (such as CPU cycles, main memory, and file storage) may have special allocation code, others (such as I/O devices) may have general request and release code
    • Accounting -To keep track of which users use how much and what kinds of computer resources
    • Protection and security -The owners of information stored in a multiuser or networked computer system may want to control use of that information, concurrent processes should not interfere with each other
      Protection involves ensuring that all access to system resources is controlled
      Security of the system from outsiders requires user authentication, extends to defending external I/O devices from invalid access attempts
      If a system is to be protected and secure, precautions must be instituted throughout it. A chain is only as strong as its weakest link.