Services of OS.ppt Two types of services
- 1. Mrs. Aparna S.Kamate Department of Computer Science and Engineering Subject-Operating System
- 2. Operating-System Structures Operating-System Structures • This chapter deals with how operating systems are structured and organized. • Different design issues and choices are examined and compared, and the basic structure of several popular OSes are presented.
- 3. Operating-System Services Operating-System 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, of course, 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.
- 4. A view of operating system services
- 5. User Interfaces User Interfaces • Means by which users can issue commands to the system. • Depending on the system these may be a command-line interface ( e.g. sh, csh, ksh, tcsh, etc. ), a GUI interface ( e.g. Windows, X-Windows, KDE, Gnome, etc. ), or a batch command systems. • The latter are generally older systems using punch cards of job-control language, JCL, but may still be used today for specialty systems designed for a single purpose.
- 6. User Operating-System Interface User Operating-System Interface Command Interpreter • Gets and processes the next user request, and launches the requested programs. • In some systems the CI may be incorporated directly into the kernel. • More commonly the CI is a separate program that launches once the user logs in or otherwise accesses the system. • UNIX, for example, provides the user with a choice of different shells, • Different shells provide different functionality, in terms of certain commands that are implemented directly by the shell without launching any external programs.
- 7. The Bourne shell command interpreter The Bourne shell command interpreter in Solaris 10 in Solaris 10
- 8. Batch Interfaces Batch Interfaces • Batch interface allows a command environment which gets execute one by one sequentially. • User creates a batch file which contains multiple executable commands in a sequence. • This batch file is executable to execute the set of commands included in it.
- 9. Graphical User Interface, GUI Graphical User Interface, GUI • Generally implemented as a desktop metaphor, with file folders, trash cans, and resource icons. • Icons represent some item on the system, and respond accordingly when the icon is activated. • First developed in the early 1970's at Xerox PARC research facility. • In some systems the GUI is just a front end for activating a traditional command line interpreter running in the background. • In others the GUI is a true graphical shell in its own right.
- 10. Slide 10 Services of O.S. Services of O.S. OSes provide environments in which programs run, and services for the users of the system, including: User Interface Program Execution I/O Management File system manipulation Communication Error detection Accounting Protection Resource Allocation
- 11. Services For User Services For User Program Execution I/O Management File system manipulation Communication Error detection
- 12. Program Execution Program Execution • The OS must be able to load a program into RAM, run the program, and terminate the program, either normally or abnormally. • 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 error).
- 13. I/O Operations I/O Operations • The OS is responsible for transferring data to and from I/O devices, including keyboards, terminals, printers, and storage devices. • A running program may require I/O, which may involve a file or an I/O device. • For specific devices, special functions may be desired (such as recording to a CD or DVD drive or blanking a CRT screen). • For efficiency and protection, users usually cannot control I/O devices directly. • Therefore, the operating system must provide a means to do I/O.
- 14. File-System Manipulation File-System Manipulation • In addition to raw data storage, the OS is also responsible for maintaining directory and subdirectory structures, mapping file names to specific blocks of data storage, and providing tools for navigating and utilizing the file system. • The file system is of particular interest. Obviously, programs need to read and write files and directories. • 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 directories based on file ownership.
- 15. Communications Communications • Inter-process communications, IPC, either between processes running on the same processor, or between processes running on separate processors or separate machines. • May be implemented as either shared memory or message passing, ( or some systems may offer both. )
- 16. Error Detection Error Detection • Both hardware and software errors must be detected and handled appropriately, with a minimum of harmful repercussions. • Some systems may include complex error avoidance or recovery systems, including backups, RAID drives, and other redundant systems. • Debugging and diagnostic tools aid users and administrators in tracing down the cause of problems.
- 17. Services for OS Services for OS • Other systems aid in the efficient operation of the OS itself: Accounting Protection Resource Allocation
- 18. Resource Allocation Resource Allocation • E.g. CPU cycles, main memory, storage space, and peripheral devices. • Some resources are managed with generic systems and others with very carefully designed and specially tuned systems, customized for a particular resource and operating environment.
- 19. Accounting Accounting • We want to keep track of which users use how much and what kinds of computer resources. • Keeping track of system activity and resource usage, either for billing purposes or for statistical record keeping that can be used to optimize future performance.
- 20. Protection and Security Protection and Security • Preventing harm to the system and to resources, either through wayward internal processes or malicious outsiders. • Authentication, ownership, and restricted access are obvious parts of this system. • Highly secure systems may log all process activity down to excruciating detail, and security regulation dictate the storage of those records on permanent non-erasable medium for extended times in secure ( off-site ) facilities.