1. Lecture 18: Operating Systems Intro to IT COSC1078 Introduction to Information Technology Lecture 18 Operating Systems James Harland james.harland@rmit.edu.au

2. Lecture 18: Operating SystemsIntro to IT Introduction to IT 1-4 Introduction, Images, Audio, Video 5-6 Computer Fundamentals Assignment 1, WebLearn Test 1 7 Review 8 Operating Systems WebLearn Test 2 9 Operating Systems Assignment 2 10 Internet 11 Internet Security WebLearn Test 3 12 Future of ITAssignment 3, Peer and Self Assessment

3. Lecture 18: Operating SystemsIntro to IT Overview  Questions?  Assignment 2  Operating Systems  Questions?

4. Lecture 18: Operating SystemsIntro to IT Assignment 2  Now in the Learning Hub  Assumes you are using Audacity  If not, please see me asap  Seems a lot, but shouldn’t be too hard once you have Audacity and your files  CD task requires CD reading software Windows: ImgBurn www.imgburn.com Mac: Burn, Toast Linux: ImgBurn via Wine, or K3B, Brasero, Nero, …

5. Lecture 18: Operating SystemsIntro to IT Processes

6. Lecture 18: Operating SystemsIntro to IT Processes A program is a static set of instructions A processes is the execution of a program, which changes state over time.

7. Lecture 18: Operating SystemsIntro to IT Processes Switching Ready Waiting Scheduler maintains process table

8. Lecture 18: Operating SystemsIntro to IT Processes Switching

9. Lecture 18: Operating SystemsIntro to IT Interrupts  Signals to the CPU  Often generated by timing circuits  CPU reacts by jumping to appropriate memory location  Dispatcher  selects a ready process  resets timing circuit  starts process  CPUs often designed to switch process states efficiently

10. Lecture 18: Operating SystemsIntro to IT Interrupts  Provide mechanism to switch processes  CPU doesn’t have to wait for I/O transfers  Switching leads to faster throughput  `Save document’ means CPU does something else while the save takes place

11. Lecture 18: Operating SystemsIntro to IT Memory Management Memory Disk Mine! STOP IT!

12. Lecture 18: Operating SystemsIntro to IT Virtual Memory What if memory requirements exceed memory size?  Pretend we have more!  Shuffle required parts (pages) between disk and memory  Not every memory cell is needed all the time…

13. Lecture 18: Operating SystemsIntro to IT Virtual Memory DiskPhysical Memory ProcesssorProcesssor

14. Lecture 18: Operating SystemsIntro to IT Co-ordination and locking MINE! Works fine for one resource …

15. Lecture 18: Operating SystemsIntro to IT Deadlock Deadlock: neither can get both resources

16. Lecture 18: Operating SystemsIntro to IT Deadlock requirements Deadlock requires: 1.Competition for nonshareable resources 2.Processes request multiple resources sequentially 3.Resources cannot be forcibly retrieved Avoid deadlock by preventing 1 or 2 Detect and correct deadlock by falsifying 3

17. Lecture 18: Operating SystemsIntro to IT Deadlock avoidance Spooling makes nonshareable resources look like shareable ones …

18. Lecture 18: Operating SystemsIntro to IT Operating Systems  Highly complex software systems  30-40 million lines of code  Lots of processes associated with them  Probably most sophisticated software ever written  Not many of them around …

19. Lecture 18: Operating SystemsIntro to IT Operating Systems

20. Lecture 18: Operating SystemsIntro to IT Conclusion  Work on Assignment 2  Web Quizzes and Web Test 2  Finish reading book!