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Chapter 1: Introduction

Topics. What is an operating system Computer System Components History of operating systems Operating system concepts Operating system structure. Chapter 1: Introduction. Reference: Operating Systems Design and Implementation (2 nd edition)

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Chapter 1: Introduction

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  1. Topics What is an operating system Computer System Components History of operating systems Operating system concepts Operating system structure Chapter 1: Introduction Reference: Operating Systems Design and Implementation (2nd edition) by Andrew S. Tanenbaum and Albert S. Woodhull

  2. What is an Operating System(1) • 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.

  3. What is an Operating System(2) • It is an extended machine • Hides the messy details which must be performed • Presents user with a virtual machine, easier to use • It is a resource manager • Each program gets time with the resource • Each program gets space on the resource

  4. Computer System Components • Hardware • Provides basic computing resources (CPU, memory, I/O devices). • Operating system • Controls and coordinates the use of the hardware among the various application programs for the various users. • 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). • Users • people, machines, other computers.

  5. Abstract View of System Components

  6. Architecture of Unix System Other Application Programs who kernel Hardware vi date

  7. History of Operating Systems (1) • 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

  8. History of Operating Systems (2) 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

  9. History of Operating Systems (3) Structure of a typical FMS job – 2nd generation

  10. History of Operating Systems (4) • Multiprogramming system • three jobs in memory – 3rd generation

  11. Operating System Concept • Processes • Files • System Calls • The shell

  12. Operating System Concept: Process(1) • A process is basically a program in execution • Each process is associated with its address space which contains code segment, data segment, stack segment etc.) • A process can open several files. • Multitasking operating system • Can run multiple processes concurrently. Example: UNIX, LINUX,WINDOWS • A process table is maintained by Operating System (OS) to keep track of these processes.

  13. Operating System Concept: Process(2) • A process can create one or more child processes • A created two child processes, B and C • B created three child processes, D, E, and F • Inter Process Communication (IPC) • Sometimes it is needed to communicate between two processes.

  14. Operating System Concept: Process(3) Two processes connected by a pipe

  15. Operating System Concept: File(1) • A directory groups files/subdirectory together • A directory has entry for files and subdirectory • Each process has a file descriptor table (FDT) to keep track of its open files.

  16. Operating System Concept: File(2) File system for a university department

  17. Operating System Concept: File(3) • Before mounting, • files on floppy are inaccessible • After mounting floppy on b, • files on floppy are part of file hierarchy

  18. Operating System Concept: System Call(1) • The interface between the OS and the user program is defined by a set of instructions called System calls. • Example • count = read(file,buffer,nbyte)

  19. Operating System Concept: System Call(2)

  20. Operating System Concept: System Call(3)

  21. Operating System Concept: System Call(4)

  22. Operating System Concept: System Call(5)

  23. Operating System Concept: System Call(6) Some Win32 API calls

  24. Operating System Concept: Shell(1) • It is the primary interface between a user sitting at his terminal and the OS. • Though it is not a part of the OS, it serves as a good example of how the system calls cab be used. • When a user logs in, a shell is started up.

  25. Operating System Concept: Shell(2) • If the user now types date for example, the shell creates a child process and runs the date program as the child. • While the child process is running, the shell waits for it to terminate. • When the child finishes, the shell types the prompt again and tries to read the next input.

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