What is an Operating System? Various systems and their pros and cons E.g. multi-tasking vs. Batch

2. What is an Operating System? • Various systems and their pros and cons • E.g. multi-tasking vs. Batch • OS definitions • Resource allocator • Control program • Kernel

3. Abstract View of System Components

4. Important OS Features/services • Process Management (CPU scheduling) • Main Memory Management • File Management • I/O System Management • Secondary Management • Networking • Protection System • Command-Interpreter System

5. Memory Tables Process Image Memory I/O Tables User data User program System stack PCB I/O File File Tables Processes Primary Table Process 1 Process 2 … Process N OS Control Structure

6. New Ready Running Exit Suspend Blocked Process State Diagram dispatch admit time-out release activate event wait suspend

7. System call vs. System program

8. Dual mode operation & why ?

9. OS structure & Layered Approach • The operating system is divided into a number of layers (levels), each built on top of lower layers. The bottom layer (layer 0), is the hardware; the highest (layer N) is the user interface. • With modularity, layers are selected such that each uses functions (operations) and services of only lower-level layers.

10. UNIX System Structure

11. Process Management • Process vs. Thread creation • Process scheduling • Process Termination • Unix process creation fork() & exec() • Identify parent vs. child • How to find out process infomation

12. Process Control Block (PCB)

13. Process vs. Thread creation

14. Multithreading Models • Many-to-One • One-to-One • Many-to-Many ---------------------------------------------- • Pthread, JAVA thread, Kernel vs. User thread

15. CPU Switch From Process to Process

16. Process Scheduling Queues • Job queue – set of all processes in the system. • Ready queue – set of all processes residing in main memory, ready and waiting to execute. • Device queues – set of processes waiting for an I/O device. • Process migration between the various queues.

17. Representation of Process Scheduling

18. Schedulers • Long-term scheduler (or job scheduler) – selects which processes should be brought into the ready queue. • Short-term scheduler (or CPU scheduler) – selects which process should be executed next and allocates CPU. • Midterm scheduler

19. Addition of Medium Term Scheduling

20. Context Switch • When CPU switches to another process, the system must save the state of the old process and load the saved state for the new process. • Context-switch time is overhead; the system does no useful work while switching. • Time dependent on hardware support.

21. Process scheduling

22. Process scheduling Concepts • Maximum CPU utilization obtained with multiprogramming • CPU–I/O Burst Cycle – Process execution consists of a cycle of CPU execution and I/O wait. • CPU burst distribution • Pre-emptive and none-preemptive

23. Scheduling Criteria • CPU utilization – keep the CPU as busy as possible • Throughput – # of processes that complete their execution per time unit • Turnaround time – amount of time to execute a particular process (finishing time – arrival time) • Waiting time – amount of time a process has been waiting in the ready queue • Response time – amount of time it takes from when a request was submitted until the first response is produced, not output (for time-sharing environment)

24. Various scheduling algorithms • FCFS • SJF • SRTF • R-R with quantum • Priority • Multi-level Priority • --------------- • Pros and cons, different conditions (q time, starvation prevention etc.) • Example of process arrival rate

25. Process Communication • IPC & Unix IPC • Client-Server • Raw socket • High-level comm (e.g. RPC, RMI, CORBA etc) • Pros & con on various mechanisms

26. Process Synchronization & deadlocks • Critical Section • Semaphore & implementation (Unix) • Spin lock and sleep(wait) lock • Deadlock • Mutex, hold-wait, no-preemption, circular-wait • Identify deadlock from resource allocation graph or code

27. Memory Management • Swapping • Contiguous Allocation • Paging • Segmentation • Segmentation with Paging • -------------------- • Pros and cons • Address translation

28. Pros & cons • Paging vs Contiguous • Hierarchical Paging vs. Hashed Page Tables vs. Inverted Page Tables

29. Example of address translation (segmetation)

30. Example of address translation

31. Virtual Memory

32. Virtual Memory • Demand paging • Demand segmentation • Page fault and how to handle • Page replacement

33. File Management • File structure • File Attributes (FCB) • directory • Access method • Access control

34. A Typical File Control Block

35. Virtual File System

36. Allocation Methods • An allocation method refers to how disk blocks are allocated for files: • Contiguous allocation • Linked allocation • Indexed allocation

37. I/O system • I/O Hardware • Application I/O Interface • Kernel I/O Subsystem • Chracter vs. block • Polling vs. interupt

38. User program & Kernel interface Note: This picture is excerpted from Write a Linux Hardware Device Driver, Andrew O’Shauqhnessy, Unix world

39. Two I/O Methods Synchronous Asynchronous Pooling or interrupt

40. LKM • What is it? • Pros & cons (vs. recompile and patches)