Chapter 11 Operating Systems

1. Chapter 11Operating Systems

2. Outline • Functional overview of an operating system • Process management • Resource allocation • CPU allocation • Memory allocation • Interprocess communication

3. Operating System Overview • Operating System Management Functions • Operating System Layers

4. Operating System Overview • The operating system oversees all hardware resources and allocates them to user and applications as needed. • The operating system performs many low-level tasks on behalf of users and application programs.

5. Operating System Overview Operating System Management Functions The operating system manages: • Hardware resources • Users and their programs

7. Operating System Overview Operating System Layers • Command Layer • Service Layer • Kernel

8. Operating System Layers

9. Operating System Layers Operating System Layers • Command Layer – the user’s interface to the operating system. • Service Layer – contains a set of functions called by application programs and the command layer. • Kernel – manages resources and directly interacts with computer hardware.

10. Outline • Functional overview of an operating system • Process management • Resource allocation • CPU allocation • Memory allocation • Interprocess communication

11. Process Management Process Control Data Structures • A process is a unit of executing software that is managed independently by the operating system. • A process can request and receive hardware resources and operating system services.

12. Process Management Process Control Data Structures • Process Control Block (PCB) – keeps track of each process by creating and updating a data structure. • The PCB is created when the process is created, updated when the process changes and deleted when the process terminates.

13. Process Management Data included in a PCB: • A unique process identification number • The current state of the process • Events for which the process is waiting • Resources allocated exclusively to the process • Machine resources consumed • Process ownership and/or access privileges • Scheduling priority

14. Process Management Threads • A portion of a process that can be scheduled and executed independently. • Process light • Thread can execute concurrently on a single processor or simultaneously on multiple processors.

15. Outline • Functional overview of an operating system • Process management • Resource allocation • CPU allocation • Memory allocation • Interprocess communication

16. Resource Allocation • Single Process Resource Allocation • Multiple Process Resource Allocation • Resource Allocation Processes • Real and Virtual Resources

17. Resource Allocation Single Process Resource Allocation • Involves only two executing programs – application and operating system. • When an application program begins executing, the operating system grants it control of all unused resources.

18. Resource Allocation Single Process Resource Allocation • Most service calls are actually indirect requests for system resources. • MS-DOS is a single-tasking operating system.

19. Resource Allocation Multiple Process Resource Allocation • Multitasking operating systems are the norm for general-purpose computers. • Multitasking operating systems must be able to handle multiple programs and users.

20. Resource Allocation Multiple Process Resource Allocation • A multitasking operating system manages hardware resources to achieve the following: • Meet the resource needs of processes • Prevent processes from interfering with one another • Efficiently use hardware and other resources

21. Resource Allocation Resource Allocation Processes • Keeps detailed records of available resources. • Knows which resource are used to satisfy which requests. • Schedules resources based on specific allocation policies to meet present and anticipated demands. • Updates records to reflect resources commitment and release by processes and users.

22. Resource Allocation Real and Virtual Resources • Real resource – a computer system’s physical devices and associated system software. • Virtual resource – the resources that are apparent to a process or user.

23. Real and Virtual Resources Providing virtual resources that meet or exceed resources is accomplished by: • Rapidly shifting resources unused by one process to other processes that need them. • Substituting one type of resource for another when possible and necessary.

24. CPU Allocation • Thread States • Interrupt Processing • Scheduling

25. CPU Allocation • A thread controls the CPU for no more than a few milliseconds before it relinquishes control and the operating system gives another thread a turn. • CPU sharing is called concurrent execution or interleaved execution.

26. CPU Allocation

27. CPU Allocation Thread States • Ready • Running • Blocked

28. CPU Allocation

29. CPU Allocation Ready State – a thread is waiting for access to a CPU. Running State – the thread has control of the CPU. • The thread or its parent process terminates normally • An interrupt occurs Block State – the thread is suspended while an interrupt is being processed.

30. CPU Allocation Interrupt Processing • A blocked thread is waiting for an event to occur. • If the event is the correction of an error and it can be corrected, the thread remains in the blocked state until the error condition is resolved; otherwise, the thread is halted.

31. Scheduling • Preemptive Scheduling • Priority-based Scheduling • Real-time Scheduling

32. Scheduling Preemptive Scheduling • A thread can be removed involuntarily from the running state. • A running process controls the CPU by controlling the content of the instruction pointer. • CPU control is lost whenever an interrupt is received.

33. Scheduling

34. Scheduling

35. Scheduling Priority-Based Scheduling Methods: • First come First served • Explicit priority • Shortest time remaining

36. Scheduling Priority-Based: First come first served: • The scheduler always dispatches the ready thread that has been waiting the longest.

37. Scheduling Priority-Based: Explicit priority: • Uses a set of priority levels and assigns a level to each process or thread. • The scheduling method can use priority levels in two ways: • Always dispatch the highest priority ready thread • Assign larger time slices to high priority threads

38. Scheduling Priority-Based: Shortest time remaining: • Chooses the next process to be dispatched based on the expected amount of CPU time needed to complete the process.

39. Scheduling Real-Time Scheduling: • Guarantees a minimum amount of CPU time to a thread if the thread makes an explicit request when it is created. • Used when a thread must have enough resources to complete its function within a specified time.

40. Technology Focus Windows 2000 Scheduling

41. Technology Focus

42. Memory Allocation • Single-Tasking Memory Allocation • Multitasking Memory Allocation • Memory Fragmentation • Noncontiguous Memory Allocation • Virtual Memory Management • Memory Protection • Memory Management Hardware

43. Memory Allocation Single-Tasking Memory Allocation – Contiguous Memory Allocation • The bulk of the operating system occupies lower memory addresses. • The application program is loaded above the operating system. • The remaining space is available for user programs and data.

44. Memory Allocation

45. Memory Allocation Single-Tasking Memory Allocation – Noncontiguous Memory Allocation • To conserve physical memory, some operating system components are loaded into memory only when needed. • When loaded, they usually are placed in upper memory.

46. Memory Allocation

47. Memory Allocation Multitasking Memory Allocation The goals of multitasking memory allocation are: • Allow as many active processes as possible. • Respond quickly to changing memory demands of processes. • Prevent unauthorized changes to a process’s memory region(s). • Implement memory allocation and addressing as efficiently as possible.

48. Memory Allocation

49. Memory Allocation

50. Memory Allocation