1. OSes: 1. Intro 1 Operating Systems v Objectives –introduce Operating System (OS) principles Certificate Program in Software Development CSE-TC and CSIM, AIT September -- November, 2003 1. Introduction (Chapter 1, S&G)

2. OSes: 1. Intro 2 Contents 1.What is an OS? 2.Some History –early systems, batch systems, multiprogramming, time-sharing, desktop systems 3.Recent Trends –multiprocessor systems, distributed, clustered, real-time, handheld, etc.

3. OSes: 1. Intro 3 1. What is an OS? Application Programs Operating System Computer Hardware compilereditor ….. database User 1User 2User N …..

4. OSes: 1. Intro 4 Features v An OS is a program that acts as an intermediary between users and hardware –supports a high-level work environment –makes hardware convenient to use –makes efficient use of hardware v OS design goals are often contradictory continued

5. OSes: 1. Intro 5 v The OS manages resources –e.g. CPU time, memory, files, I/O devices –avoid bottlenecks –keeps the hardware busy v The OS controls –prevents users/programs adversely affecting the hardware or other users –the system should never crash

6. OSes: 1. Intro 6 OS Development

7. OSes: 1. Intro 7 2. Some History v 2.1. Early Systems v 2.2. Batch Systems v 2.3. Multiprogramming Batch Systems v 2.4. Time-Sharing v 2.5. Desktop Systems

8. OSes: 1. Intro 8 2.1. Early Systems v One person at a contol panel of switches and lights v Load libraries/utilities from tape v Slow set-up v Very costly hardware ComputeReadPrint ComputeReadPrint

9. OSes: 1. Intro 9 2.2. Batch Systems v Motivation: highly utilise the hardware –dedicated computer operator –card/tapes handed to the operator v Similar jobs were run in sequence (batched) –no machine/user interaction –errors were recorded as a printed core dump –very slow turnaround time (for users)

10. OSes: 1. Intro 10 Resident Monitor v For automatic job sequencing LoaderJob Sequencing Control Card Interpreter User Program Area monitor

11. OSes: 1. Intro 11 $END data cards $RUN program cards Control Cards v User’s cards included control cards to guide the monitor. $JOB

12. OSes: 1. Intro 12 Off-line I/O Processing Card Reader CPU Line Printer On-line: Card Reader CPU Line Printer Off-line: tape drives

13. OSes: 1. Intro 13 Spooling Card Reader CPU Line Printer disk I/O v Job pool on disk, scheduled by OS

14. OSes: 1. Intro 14 Benefit Of Spooling ComputeReadPrint ComputeReadPrint ComputeReadPrint

15. OSes: 1. Intro 15 2.3. Multiprogrammed Batch Systems v Have several jobs in memory at a time. v Multiprogramming allows the OS to switch to executing another job when the current one is suspended (e.g. waiting for user input). v The OS may also swap jobs to/from disk. v Requires CPU scheduling

16. OSes: 1. Intro 16 2.4. Time-Sharing v Multiple jobs are executed by the CPU switching between them –as in multiprogramming v Difference is speed; the switching is so fast that users feel that their programs are always running. v Executing program is called a process. continued

17. OSes: 1. Intro 17 v Virtual memory –hides the distinction between memory and disk v Disk management v Concurrent execution requires fancy scheduling schemes v Job synchronisation, communication, deadlock avoidance

18. OSes: 1. Intro 18 2.5. Desktop Systems v Personal computers –computer system dedicated to a single user v I/O devices –keyboards, mice, display screens, small printers v User convenience and responsiveness continued

19. OSes: 1. Intro 19 v Can adopt technology developed for larger operating system –sole use means less need for protection features v May run several different types of operating systems –e.g. Windows, MacOS, UNIX, Linux

20. OSes: 1. Intro 20 3. Recent Trends 3.1. Multiprocessor Systems 3.2. Distributed Systems 3.3. Clustered Systems 3.4. Real-time Systems 3.5. Handheld Systems 3.6. Computing Environments

21. OSes: 1. Intro 21 3.1. Multiprocessor Systems v A system with more than 1 processor, but perhaps sharing computer bus, clock, memory and devices –tightly coupled systems v n processes = n times speed-up continued

22. OSes: 1. Intro 22 v Benefits: –save money on hardware –increased reliability (graceful degradation) v Two main types: –symmetric multiprocessing systems –asymmetric multiprocessing systems

23. OSes: 1. Intro 23 3.1.1. Symmetric Multiprocessing v Each processor runs an identical copy of the OS v Often in a master-slave configuration v Jobs/resources are shared dynamically for better load balancing

24. OSes: 1. Intro 24 3.1.2. Asymmetric Multiprocessing v Have dedicated processors for specific tasks –e.g. remote job entry (RJE), I/O terminal buffering

25. OSes: 1. Intro 25 3.2. Distributed Systems v “The system is the network.” continued

26. OSes: 1. Intro 26 v Multiprocessors, but not sharing memory, clock, etc. –may be geographically separated –loosely coupled systems v Benefits: –resource sharing, speed-up, reliability –matches modern business practise

27. OSes: 1. Intro 27 3.3. Clustered Systems v Clustering allows two or more systems to share storage. –provides high reliability v Asymmetric clustering –one host runs the application while others standby v Symmetric clustering –all hosts run the application

28. OSes: 1. Intro 28 3.4. Real-time Systems v There are time constraints placed on operations/data flows which must be met. v Uses: –scientific experiments, medicine, industrial control systems, home appliances, weapons v Two types: –hard real-time systems –soft real-time systems

29. OSes: 1. Intro 29 3.4.1. Hard Real-time Systems v Critical tasks are guaranteed to be done on time. v Many useful hardware/OS features are missing since they make the time constraints too hard to satisfy –e.g. no secondary storage

30. OSes: 1. Intro 30 3.4.2. Soft Real-time Systems v Critical tasks are given priority, but their time constraints may not be met. v Weaker, but can be used alongside typical OS features v Applications: VR, multimedia

31. OSes: 1. Intro 31 3.5. Handheld Systems v Personal Digital Assistants (PDAs) v Cellular telephones v Issues: –limited memory –slow processors –small display screens

32. OSes: 1. Intro 32 3.6. Computing Environments v Changing environments are leading to changes in OS requirements –traditional –hand-held, mobile –Web-based –embedded, dedicated processors