1. CS4315A. Berrached:CMS:UHD1 Operating System Structures Chapter 3

2. CS4315A. Berrached:CMS:UHD2 Operating System Structures OS Design Constraints OS Basic Functions OS Structures

3. CS4315A. Berrached:CMS:UHD3 Design Constraints Performance Protection & Security Correctness Maintainability Commercial factors

4. CS4315A. Berrached:CMS:UHD4 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

5. CS4315A. Berrached:CMS:UHD5 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.

6. CS4315A. Berrached:CMS:UHD6 OS Basic Functions Device management Process & resource management Memory Management File Management

7. CS4315A. Berrached:CMS:UHD7 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

8. CS4315A. Berrached:CMS:UHD8 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

9. CS4315A. Berrached:CMS:UHD9 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

10. CS4315A. Berrached:CMS:UHD10 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

11. CS4315A. Berrached:CMS:UHD11 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

12. CS4315A. Berrached:CMS:UHD12 Basic OS Functions

13. CS4315A. Berrached:CMS:UHD13 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).

14. CS4315A. Berrached:CMS:UHD14 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.