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Operating System Structures

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  1. Operating System Structures Chapter 3 A. Berrached:CMS:UHD

  2. Operating System Structures • OS Design Constraints • OS Basic Functions • OS Structures A. Berrached:CMS:UHD

  3. Design Constraints • Performance • Protection & Security • Correctness • Maintainability • Commercial factors A. Berrached:CMS:UHD

  4. Performance • People use computers for the potential of rapid information processing • There are several measures of performance • throughput • response time • The OS is an overhead function => should not use too much of machine resources • Provide an environment in which programmers can produce solutions in a cost-effective manner ==> trade off A. Berrached:CMS:UHD

  5. Correctness & Maintainability • Correctness - refers to whether OS functions meet their requirements. • Correctness is the most basic requirement on which all other requirement are based- e.g. security depends on correct operation of OS => trusted vs un-trusted software • Maintainability - refers to the ease with which software can be changed/extended, bugs can be fixed, etc. A. Berrached:CMS:UHD

  6. OS Basic Functions • Device management • Process & resource management • Memory Management • File Management A. Berrached:CMS:UHD

  7. Device Management • OS Manages the allocation, sharing and isolation of I/O devices (disks, tapes, terminals, etc.) • Most Operating Systems treat all devices in the same general manner • UNIX treats them all like files • Chapters 4 & 5 discuss Device Management A. Berrached:CMS:UHD

  8. Process & Resource Management • A process is the basic unit of computation • Resources are the elements needed by a process so that it can execute • CPU, Memory, I/O devices, data etc. • OS provides a set of process management mechanisms: for process creation , blocking, resumption, termination ,etc A. Berrached:CMS:UHD

  9. Process & Resource Management • OS manages computer resources so that multiple processes can execute simultaneously • CPU scheduling • resource allocation, sharing & process synchronization • resource allocation • Chapters 6 - 10 A. Berrached:CMS:UHD

  10. Memory Management • Allocation and use of the primary memory resource • memory allocation among competing processes • enforce memory isolation and sharing • Most modern OS support virtual memory. • Virtual memory allows processes to access data in secondary storage as if it were in main memory. • Chapter s11&12 A. Berrached:CMS:UHD

  11. File Management • Information that need to be saved "permanently" must be stored in a secondary storage device e.g. a disk, tape, etc. • Files are an abstraction of secondary storage devices • File manager is responsible for • managing the file system: file & directory creation and manipulation • mapping files into physical storage devices A. Berrached:CMS:UHD

  12. Basic OS Functions A. Berrached:CMS:UHD

  13. OS Structures-Simple Approach • MS-DOS - written to provide the most functionality in the least space • not divided into modules • Although MS-DOS has some structures, its interfaces and levels of functionality are not well separated. • application programs are able to access BIOS routines directly (bypassing DOS). A. Berrached:CMS:UHD

  14. OS Structures--UNIX • UNIX -- modular • UNIX consists of two separate parts: • System programs (Shells and commands, compilers and interpreters, system libraries) • The kernel: part of OS that is most critical to its correct operation (trusted) • provides CPU scheduling, memory management, file management, and other operating system functions. A. Berrached:CMS:UHD