1. CSS430 Introduction Textbook Ch1 – Ch2 These slides were compiled from the OSC textbook slides (Silberschatz, Galvin, and Gagne) and the instructor’s class materials. CSS430 Introduction

2. Course Objectives • You will: • Study the fundamental concepts of operating systems • Practice the logical design using Java • But not: • Learn how to use/hack Windows and Linux • If this is your main objective, you should take R140/145/R708 of UW Computing Training http://www.washington.edu/computing/training • Skill up system programming with C++ • Program 1 will deal with several system calls, but if this is your main interest, you should take CSS432, CSS434 or other C++ programming courses. CSS430 Introduction

3. Other Noteworthy OSes • Distributed OSes • All blends of *NIX • Any windows competitor • IBM PS/2 • NeXT OS • Commodore 64 • Embedded OSes • Low-power OSes CSS430 Introduction

4. Important Time Lines • Program 1: System calls and shell • Program 2: Scheduler • Midterm: Process Management • Program 3: Synchronization • Program 4: Paging • Final: Memory/File Management • Project: Unix-like file system (Check the syllabus for their due dates.) CSS430 Introduction

5. Important Web Pages and Email Addresses • Our class web: http://courses.washington.edu/css430/index.html • Java: http://java.sun.com/j2se/1.4/docs/api/index.html • Instructor’s email: {mfukuda, ksung, or rynn}@u.washington.edu • Class discussion mailing list: Use the message board. • Assignment submission: Use Catalyst drop box. CSS430 Introduction

6. What is an Operating System • Goals • Making the computer system convenient to use • Using computer hardware in an efficient manner • 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) CSS430 Introduction

7. Computer System Components CSS430 Introduction

8. OS - Intermediary • The OS acts on our behalf as a micro-manager • An OS acts as an intermediary between the computer and the user • It should use resources fairly and efficiently; ease of use • It should protect users from one another, and from the kernel CSS430 Introduction

9. From the Text • “an OS is similar to a government” CSS430 Introduction

10. More from the Dino Book • “Like a government, the OS performs no useful function by itself” CSS430 Introduction

11. O.S. & Computer Architecture • As hardware is introduced, Oses are built to make the hardware useable • As Oses evolve, it becomes obvious that certain hardware elements could simplify the operation of the kernel • So, a back-and-forth cycle exists. CSS430 Introduction

12. Operating Systems History • Batch systems: • Multiprogramming: IBM360 • Time-sharing systems: Multics, Unix • Personal-computer systems: Windows, Linux • Distributed systems: Amoeba, Mach CSS430 Introduction

13. Batch Systems • A job is assembled of the program, the data, and some control information (in control cards). • Programmers pass their jobs to an operator. • The operator batched together jobs. • OS transfers control from one job to another. • Each job output is sent back to the programmer. CSS430 Introduction

14. Multiprogramming • Several jobs are kept in main memory at the same time. • OS picks one of them to execute. • The job may have to wait for a slow I/O operation to complete. • OS switches to and executes another job. • To facilitate multiprogramming, OS needs: • Job scheduling • Memory management CSS430 Introduction

15. Time-Sharing Systems • This is a logical extension of multiprogramming. • Each user has at least one separate program in memory. • A program in execution is referred to as a process. • Process switch occur so frequently that the users can interact with each program while it is running. • File system allows users to access data and program interactively. CSS430 Introduction

16. Personal-Computer Systems • Personal computers – computer system dedicated to a single user. • User convenience and responsiveness • Can adopt technology developed for larger operating systems’ some features. • At its beginning, a single user system didn’t not need advanced CPU utilization and protection. • Later, file protection is necessary to avoid virus. • Overall, the same OS concepts are appropriate for the various different classes of computers. CSS430 Introduction

17. Parallel Systems • Multiprocessor systems with more than one CPU in close communication (in one box). • Tightly coupled system– processors share memory and a clock; shared-memory-based communication. • Advantages of parallel system: • Increased throughput • Economical • Increased reliability CSS430 Introduction

18. Distributed Systems • Loosely coupled system– each processor has its own local memory; message-based communication through various communications lines, such as SAN, LAN, WAN or telephone lines. • Advantages of distributed systems. • Resources Sharing (Printer, DB, special devices) • Performance (load sharing, process migration) • Reliability • Communications • http://directory.google.com/Top/Computers/Software/Operating_Systems/Network/Distributed/ CSS430 Introduction

19. Real-Time Systems • Dedicated to a single application: controlling scientific experiments, medical imaging systems, industrial, and military control systems (ex. Dam control, nuclear reactor, missile guiding, etc.). • Hard deadline • Hard real-time system. • Data stored in short-term memory or ROM • Conflicts with time-sharing systems • Soft real-time system • Best effort to meet the deadline • Useful in applications (multimedia, virtual reality, QoS) CSS430 Introduction

20. Computer Hardware CSS430 Introduction

21. requesting process waiting user device driver Interrupt handler kernel Hardware data transfer time Synchronous I/O • During execution, each program needs I/O operations to receive keyboard inputs, open files, and print out results. • At the early computer era, a program had to wait for an I/O operation to be completed. (Synchronous I/O) • This frequently causes CPU idle. CSS430 Introduction

22. requesting process continuing device driver Interrupt handler Hardware data transfer Async I/O and Interrupts • Asynchronous I/O returns control to a user program without waiting for the I/O to complete. • When the I/O is completed, an interrupt occurs to CPU that temporarily suspends the user program and handles the I/O device. user kernel time CSS430 Introduction

23. Discussions 1 • What tasks should OS perform in order to suspend and resume a program? List them. CSS430 Introduction

24. Hardware Protection • Purpose: • With resource sharing, many programs could be affected by a bug in one program. • Incorrect or malicious resource accesses cause a hardware trap to the operating system. • Dual-Mode Operation: • User mode: no privileged instructions allowed. • Kernel mode: Privileged instructions allowed. • I/O Protection: all privileged • Memory Protection: A region from the base to the limit register allowed to use • CPU Protection: CPU allowed to use until the timer gets 0. CSS430 Introduction

25. Dual-Mode Operations • Provide hardware support to differentiate between at least two modes of operations. 1. User mode– execution done on behalf of a user. 2. Monitor mode (also supervisor mode, system mode, or Kernel mode) – execution done on behalf of operating system. • Switching between two modes • Device interrupts, hardware traps, system calls cause a trap to the kernel mode • The operating system returns to the user mode after servicing requests. CSS430 Introduction

26. System Calls CSS430 Introduction

27. Discussions 2 • Early computers did not have interrupts, timers, and/or privileged instructions. What features was OS unable to facilitate? CSS430 Introduction

28. Discussions 3 • List three distinct events upon which OS can get back CPU from the current user program. CSS430 Introduction

29. Project 1 – System Calls & Shells • This warmup exercise has two parts: • A C/C++ app that makes direct system calls to UNIX • A Shell.java program that runs with ThreadOS CSS430 Introduction

30. Part 1 • Experiment with User-to-OS APIs • System calls in C/C++ on Unix • See the list of system calls you are to use in the assignment CSS430 Introduction

31. Part 2 • To get started, download the ThreadOS files at • /usr/apps/css430/ThreadOS/ • Grab the class files, too! • You’ll need these more than the src for hw1 CSS430 Introduction

32. Grading Guide • See http://courses.washington.edu/css430/prog/prog1.html • More on this Thursday CSS430 Introduction