COMS 4118 Operating Systems Spring 2005

1. COMS 4118Operating SystemsSpring 2005 Abhinav Kamra kamra@cs.columbia.edu http://www.cs.columbia.edu/~kamra/teaching/ Operating System Concepts Silberschatz, Galvin and Gagne 2002

2. Course Contents • Processes • Process Management • Inter-process Communication • Process Scheduling • Process Synchronization (to access very popular data) • Deadlocks • Memory Management • Virtual Memory • File Systems • I/O Systems • Interrupt Handling Operating System Concepts Silberschatz, Galvin and Gagne 2002

3. Logistics • Lectures • Tuesdays and Thursdays • 9:30am – 10:45am • Exams • No mid-term exam • 4-5 “Quizzes” • A Comprehensive Final Exam Operating System Concepts Silberschatz, Galvin and Gagne 2002

4. Logistics (continued) • Homework Assignments • None • Grading • Quizzes: 25% • Programming Assignments: 50% • Final Exam: 25% Operating System Concepts Silberschatz, Galvin and Gagne 2002

5. Logistics (continued) • Programming Assignments • 2-3 small assignments • One “big” assignment (A Real OS) • OSKit and VMWare • An MP3 CD Player OS Operating System Concepts Silberschatz, Galvin and Gagne 2002

6. Chapter 1: Introduction • What is an Operating System? • Mainframe Systems • Desktop Systems • Multiprocessor Systems • Distributed Systems • Clustered System • Real -Time Systems • Handheld Systems Operating System Concepts Silberschatz, Galvin and Gagne 2002

7. “I think that there is a world market for five computers” - Thomas J. Watson (1945) Operating System Concepts Silberschatz, Galvin and Gagne 2002

8. What is an Operating System? • A program that acts as an intermediary between a user of a computer and the computer hardware. • Operating system goals: • Execute user programs and make solving user problems easier. • Make the computer system convenient to use. • Use the computer hardware in an efficient manner. Operating System Concepts Silberschatz, Galvin and Gagne 2002

9. Why Study Operating Systems? • We want to have an efficient O/S because it • consumes more resources than any other program. • is the most complex program. • is necessary for any use of the computer. • is used by many users. • Efficiency is measured through • Functionality • Performance: Time and Utilization • Convenience and Cost Operating System Concepts Silberschatz, Galvin and Gagne 2002

10. Goals of This Course • Understand what an operating system is • Understand the key components of an operating system • Have a deeper understanding of common operating systems in the market (e.g. Windows, Unix, MS-DOS) and the issues associated with them • To be able to use performance measures Operating System Concepts Silberschatz, Galvin and Gagne 2002

11. Computer System Components 1. Hardware – provides basic computing resources (CPU, memory, I/O devices). 2. Operating system – controls and coordinates the use of the hardware among the various application programs for the various users. 3. Applications programs – define the ways in which the system resources are used to solve the computing problems of the users (compilers, database systems, video games, business programs). 4. Users (people, machines, other computers). Operating System Concepts Silberschatz, Galvin and Gagne 2002

12. Abstract View of System Components Operating System Concepts Silberschatz, Galvin and Gagne 2002

13. Operating System Definitions • Resource allocator – manages and allocates resources. • Control program – controls the execution of user programs and operations of I/O devices . • Kernel – the one program running at all times (all else being application programs). Operating System Concepts Silberschatz, Galvin and Gagne 2002

14. Operating Systems Ease the Pain • Performs the interface task with the hardware (file operations, memory paging, etc.) which should have been done by the user if the OS did not exist • High-level interface (GUI, command line a.k.a. CUI) • The O/S’s capability for multi-user and multi-tasking utilize the hardware efficiently • Makes visible the “virtual” component of the system • Allows program interaction Operating System Concepts Silberschatz, Galvin and Gagne 2002

15. Why are Operating Systems Difficult to Create and Maintain? • Size • Too big for one person; current systems have millions of lines of code and involve 10-100 man years to build • Lifetime • Operating systems remain longer than the programmers who originally wrote them. Code is written and rewritten and original intent is forgotten (Unix designed to be cute, small system - now several volumes thick!) Operating System Concepts Silberschatz, Galvin and Gagne 2002

16. Why are Operating Systems Difficult to Create and Maintain? • Complexity • The system must do difficult things -- deal with ugly I/O devices, multiplexing/juggling act, handle errors • Multitasking • Must do several things at once. • General purpose Operating System Concepts Silberschatz, Galvin and Gagne 2002

17. A Brief History: Early 1950’s, Mainframes Rule! • Early systems • No O/S! Programmer is also operator • Large machines run from a console; programs loaded through switches and card readers • Simple batch systems were the first real OS • Setup time was a problem -> hire an operator • Operator ran related jobs together • O/S was a simple program stored in one part of memory • Loads a single job from card reader into memory • Transfers control from one job to the next Operating System Concepts Silberschatz, Galvin and Gagne 2002

18. Memory Layout for a Simple Batch System Operating System Concepts Silberschatz, Galvin and Gagne 2002

19. Offline Processing Allowed jobs to be read ahead of time onto tape Card Reader CPU Line printer On-line processing Card Reader CPU Line printer Tape Drive Tape Drive Off-line processing Tape Drive Tape Drive Operating System Concepts Silberschatz, Galvin and Gagne 2002

20. History: Spooling • Allowed jobs to be read ahead onto disk • Spool (Simultaneous Peripheral Operation On-Line) disk Card Reader Line printer CPU Operating System Concepts Silberschatz, Galvin and Gagne 2002

21. Multiprogrammed Systems • Multiprogrammed batch systems provided increased utilization • Keeps several jobs in memory simultaneously • I/O processing of one job overlaps with computation of another • Analogy: Lawyer working on several cases; while waiting to go to trial on one, can work on another • Needs CPU scheduling Operating System Concepts Silberschatz, Galvin and Gagne 2002

22. Multiprogrammed Batch Systems Several jobs are kept in main memory at the same time, and the CPU is multiplexed among them. Operating System Concepts Silberschatz, Galvin and Gagne 2002

23. Timesharing/Multitasking Systems • Timesharing supported interactive use • Each user feels as if he/she has the entire machine • Tries to optimize response time • Based on time-slicing; divide CPU equally among others Operating System Concepts Silberschatz, Galvin and Gagne 2002

24. Desktop Systems • Personal computers – computer system dedicated to a single user. • I/O devices – keyboards, mice, display screens, small printers. • User convenience and responsiveness. • Can adopt technology developed for larger operating system. Often individuals have sole use of computer and do not need advanced CPU utilization of protection features. • May run several different types of operating systems (Windows, MacOS, UNIX, Linux) Operating System Concepts Silberschatz, Galvin and Gagne 2002

25. Parallel Systems • Multiprocessor systems with more than one CPU in close communication. • Tightly coupled system – processors share memory and a clock; communication usually takes place through the shared memory. • Advantages of parallel system: • Increased throughput • Economical • Increased reliability • graceful degradation • fail-soft systems (shut down non-essential components) Operating System Concepts Silberschatz, Galvin and Gagne 2002

26. Parallel Systems (Cont.) • Symmetric multiprocessing (SMP) • Each processor runs and identical copy of the operating system. • Many processes can run at once without performance deterioration. • Most modern operating systems support SMP • Asymmetric multiprocessing • Each processor is assigned a specific task; master processor schedules and allocated work to slave processors. • More common in extremely large systems Operating System Concepts Silberschatz, Galvin and Gagne 2002

27. Symmetric Multiprocessing Architecture Operating System Concepts Silberschatz, Galvin and Gagne 2002

28. Distributed Systems • Distribute the computation among several physical processors. • Loosely coupled system – each processor has its own local memory; processors communicate with one another through various communications lines, such as high-speed buses or telephone lines. • Advantages of distributed systems. • Resources Sharing • Computation speed up – load sharing • Reliability • Communications Operating System Concepts Silberschatz, Galvin and Gagne 2002

29. Distributed Systems (cont) • Requires networking infrastructure. • Local area networks (LAN) or Wide area networks (WAN) • May be either client-server or peer-to-peer systems. Operating System Concepts Silberschatz, Galvin and Gagne 2002

30. General Structure of Client-Server Operating System Concepts Silberschatz, Galvin and Gagne 2002

31. Clustered Systems • Clustering allows two or more systems to share storage. • Provides high reliability. • Asymmetric clustering: one server runs the application while other servers standby. • Symmetric clustering: all N hosts are running the application. Operating System Concepts Silberschatz, Galvin and Gagne 2002

32. Real-Time Systems • Often used as a control device in a dedicated application such as controlling scientific experiments, medical imaging systems, industrial control systems, and some display systems. • Well-defined fixed-time constraints. • Real-Time systems may be either hard or soft real-time. Operating System Concepts Silberschatz, Galvin and Gagne 2002

33. Real-Time Systems (Cont.) • Hard real-time: • Secondary storage limited or absent, data stored in short term memory, or read-only memory (ROM) • Conflicts with time-sharing systems, not supported by general-purpose operating systems. • Soft real-time • Limited utility in industrial control of robotics • Useful in applications (multimedia, virtual reality) requiring advanced operating-system features. Operating System Concepts Silberschatz, Galvin and Gagne 2002

34. Handheld Systems • Personal Digital Assistants (PDAs) • Cellular telephones • Issues: • Limited memory • Slow processors • Small display screens. Operating System Concepts Silberschatz, Galvin and Gagne 2002

35. Migration of Operating-System Concepts and Features Operating System Concepts Silberschatz, Galvin and Gagne 2002