1. Mid Term review
CSC345

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

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

7. System call vs. System program

8. Chapter 2: Computer-System Structures
Computer System Operation
I/O Structure
Storage Structure
Storage Hierarchy
Hardware Protection
General System Architecture

9. Two I/O Methods
Synchronous
Asynchronous

10. Dual mode operation & why ?

11. Use of A System Call to Perform I/O

12. Use of A Base and Limit Register

13. Hardware Address Protection

14. 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.

15. UNIX System Structure

16. 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

17. Process Control Block (PCB)

18. Process vs. Thread creation

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

20. CPU Switch From Process to Process

21. 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.

22. Representation of Process Scheduling

23. 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

24. Addition of Medium Term Scheduling

25. 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)

26. Class Exercise Process Time p1 6 P2 3 P3 7 p4 1
Each team works on finding an average turnaround time for a
quantum time at 1, 2, 3, 4, 5, 6, 7
Process
Time p1 6 P2 3 P3 7 p4 1

27. First-Come, First-Served (FCFS) Scheduling
Process Burst Time
P1 24
P2 3
P3 3
Suppose that the processes arrive in the order: P1 , P2 , P3 The Gantt Chart for the schedule is:
Waiting time for P1 = 0; P2 = 24; P3 = 27
Average waiting time: ( )/3 = 17 P1 P2 P3 24 27 30

28. Turnaround Time Varies With The Time Quantum

29. 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.

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

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