OPERATING SYSTEMS

1. Lecturer: Szabolcs Mikulas Office: B38B E-mail: szabolcs@dcs.bbk.ac.uk URL: http://www.dcs.bbk.ac.uk/~szabolcs/os.html Textbook: A.S. Tanenbaum, Modern Operating Systems, Second edition, Prentice Hall, 2001, ISBN 0-13-031358-0 OPERATING SYSTEMS

2. 1.Introduction 2. Processes and threads 3. Deadlock 4. Memory management 5. Input/output 6. File systems 7. Multimedia operating systems 8. Multiple processor systems 9. Security UNIX and Windows are to be used as running case studies. OUTLINE

3. Introduction 1.1 What is an operating system 1.2 History of operating systems 1.3 The operating system zoo 1.4 Computer hardware review 1.5 Operating system concepts 1.6 System calls 1.7 Operating system structure Chapter 1

4. Introduction • A computer system consists of • hardware • system programs • application programs

5. What is an Operating System • It is an extended, or virtual, machine • provides a simple, high-level abstraction, i.e., hides the “messy details” which must be performed • presents user with a virtual machine, easier to use • provides services; programs obtain these by system calls • It is a resource manager • provides orderly and controlled allocation for programs in terms of time and space, multiplexing

6. History of Operating Systems • First generation 1945 - 1955 • vacuum tubes, plug boards • Second generation 1955 - 1965 • transistors, batch systems • Third generation 1965 – 1980 • ICs and multiprogramming • Fourth generation 1980 – present • personal computers

7. Second Generation Early batch system • bring cards to 1401 • read cards to tape • put tape on 7094 which does computing • put tape on 1401 which prints output

8. Second Generation (2) • Structure of a typical FMS job – 2nd generation

9. Third Generation Third generation: • Multiprogramming • Timesharing • MULTICS => UNIX

10. Fourth Generation Fourth generation (1980- ) - Personal computers • MS-DOS, • Graphical User Interface (GUI), • Windows, • Network and distributed OSs

11. The Operating System Zoo • Mainframe operating systems • Server operating systems • Multiprocessor operating systems • Personal computer operating systems • Real-time operating systems • Embedded operating systems • Smart card operating systems

12. Computer Hardware Review Monitor • Components of a simple personal computer Bus

13. Processors (a) A three-stage pipeline (b) A superscalar CPU

14. Memory • Typical memory hierarchy • numbers shown are rough approximations

15. Hard Disk Structure of a disk drive

16. Base-Limit Pairs One base-limit pair and two base-limit pairs

17. Interrupt (a) Steps in starting an I/O device and getting interrupt (b) How the CPU is interrupted (a) (b)

18. Pentium System Structure of a large Pentium system

19. Processes • Program in execution • Address space: list of memory locations for read and write - code, data, stack • Process table: one entry for each process, contains: list of open files, state UID etc. • Communication, scheduling

20. A Process Tree A created two child processes, B and C B created three child processes, D, E, and F

21. Deadlock (a) A potential deadlock. (b) An actual deadlock. Read-write example

22. Main Memory Holds executing programs Multiple programs - protection Large programs - virtual memory

23. File System File system for a university department

24. Files • Abstract model of device independent files • Hierarchy, directories, operations • Absolute and relative path names - root and working directory • Special files (for I/O devices): • block s.f. • character s.f. • Security

25. Mounting • Before mounting, • files on floppy are inaccessible • After mounting floppy on b, • files on floppy are part of file hierarchy

26. Pipe Two processes connected by a pipe e.g. sort <in|head -30

27. System Calls • Interface between OS and user programs (to perform privileged operations) • Machine dependent, but procedure libraries

28. Steps in Making a System Call There are 11 steps in making the system call read (fd, buffer, nbytes)

29. Some System Calls For Process Management

30. Some System Calls For File Management

31. Some System Calls For Directory Management

32. Some System Calls For Miscellaneous Tasks

33. Shell • A stripped down shell: while (TRUE) { /* repeat forever */ type_prompt( ); /* display prompt */ read_command (command, parameters) /* input from terminal */ if (fork() != 0) { /* fork off child process */ /* Parent code */ waitpid( -1, &status, 0); /* wait for child to exit */ } else { /* Child code */ execve (command, parameters, 0); /* execute command */ } }

34. Link Link(/usr/jim/memo,/usr/ast/note) (a) Two directories before linking/usr/jim/memo to ast's directory (b) The same directories after linking

35. Mount mount(/dev/fd0,/mnt,0) (a) File system before the mount (b) File system after the mount

36. Windows System Calls Some Win32 API calls

37. Monolithic System Simple structuring model for a monolithic system

38. Layered System Structure of the THE operating system • MULTICS - concentric rings

39. Virtual Machines Structure of VM/370 with CMS CMS: Conversational Monitor System VM: Virtual Machine Monitor - multiprogramming • MS-DOS on Pentium • JVM

40. Exokernels Similar to VM, but • Restriction to allocated resources • No need for remap

41. Client-Server Model Microkernel • handles communication • provides low-level resource management Cf. Mechanism versus policy

42. C-S Model in a DS The client-server model in a distributed system