Chapter 2 Operating System Overview

1. Operating Systems:Internals and Design Principles, 6/EWilliam Stallings Chapter 2Operating System Overview

2. Operating System • A program that controls the execution of application programs • An interface between applications and hardware

3. Evolution of Operating Systems • Serial processing • No operating system • Machines run from a console with display lights, toggle switches, input device, and printer

4. Evolution of Operating Systems • Serial processing • Setup included loading the compiler, source program, saving compiled program, and loading and linking: mounting/dismounting tapes or setting up card decks • Schedule time • Problems with this type of machine sharing?

5. Evolution of Operating Systems • Simple batch system • Monitor • Software that controls the sequence of events • Batch jobs together • Program returns control to monitor when finished

6. Job Control Language • Special type of programming language • Provides instruction to the monitor • What compiler to use • What data to use

7. Hardware Features • Memory protection • Do not allow the memory area containing the monitor to be altered • Timer • Prevents a job from monopolizing the system

8. Hardware Features • Privileged instructions • Certain machine level instructions can only be executed by the monitor • Interrupts • Early computer models did not have this capability • User mode vs. Kernel mode?

9. Memory Protection • User program executes in user mode • Certain instructions may not be executed • Certain memory areas are protected from user’s use and may not be accessed

10. Memory Protection • Monitor executes in system mode • Kernel mode • Privileged instructions are executed • Protected areas of memory may be accessed

11. Limitations? • Simple batch system • Monitor • Software that controls the sequence of events • Batch jobs together • Program returns control to monitor when finished • What are the limitations?

12. System Utilization Example

13. Uniprogramming • Processor must wait for (blocked) I/O instruction to complete before preceding

14. Program Flow of Control

15. Program Flow of Control

16. Multiprogramming • When one job needs to wait for I/O, the processor can switch to the other job

17. Multiprogramming

18. Example

19. Utilization Histograms

20. Time Sharing Systems • Using multiprogramming to handle multiple interactivejobs • Processor’s time is shared among multiple users • Multiple users simultaneously access the system through terminals • How would Time Sharing Systems differ from Batch Multiprogramming Systems?

21. Batch Multiprogramming versus Time Sharing • How would you schedule the following jobs: J1(0, 100), J2(1, 10), J3(2, 3), J4(3, 5), J5(4, 2) • in a batch system • in a time-sharing system

22. CTSS Operation

23. OS Design Challenges • Time sharing and multiprogramming lead to challenges in • Process management (multiple programs time share the system, mutual exclusion, synchronization, resource contention etc) • Memory management (OS, multiple programs are in the memory) • Scheduling of processor(s) and I/O device

24. Operating System Objectives • Convenience • Efficiency • Ability to evolve

25. Four Interfaces • Figure 3-6. Various interfaces offered by computer systems.

26. Four Interfaces (1) • An interface between the hardware and software consisting of machine instructions • that can be invoked by any program

27. Four Interfaces (2) • An interface between the hardware and software, consisting of machine instructions • that can be invoked only by privileged programs, such as an operating system

28. Four Interfaces (3) • An interface consisting of system calls as offered by an operating system

29. Four Interfaces (4) • An interface consisting of library calls • Generally forming what is known as an application programming interface (API) • In many cases, the aforementioned system calls are hidden by an API

30. Layers and Views

31. Services Provided by the OS • Program development • Editors and debuggers • e.g., emacs, vi, gdb • Program execution • Load instructions & data, control scheduling • Access I/O devices • Hide the peculiar I/O instructions or control signals required for each device, access it by simple read and write function calls

32. Services Provided by the OS • Controlled access to files • Control who can access which files • System access • Protect resources and data from unauthorized users • Resolve conflicts for resource contention

33. Services Provided by the OS • Error detection and response • Internal and external hardware errors • Software errors • Operating system cannot grant request of application

34. Services Provided by the OS • Accounting • Collect usage statistics • Monitor performance • Used to anticipate future enhancements • Used for billing purposes

35. Operating System • Responsible for managing resources • Memory, processor, I/O devices • Functions same way as ordinary computer software • It is a program that is executed • Operating system relinquishes control of the processor, but directs the processor so that the processor will allow it to regain control

36. OS as Resource Manager

37. Kernel • Portion of operating system that is in main memory • Contains most frequently used functions • Also called the nucleus

38. Evolution of Operating Systems • Hardware upgrades plus new types of hardware (for instance, paging hardware)/ New services / Fixes