1 operating systems lecturer: szabolcs mikulas office: b38b e-mail: szabolcs@dcs.bbk.ac.uk url:...

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OPERATING SYSTEMS

Lecturer: Szabolcs MikulasOffice: B38BE-mail: szabolcs@dcs.bbk.ac.ukURL: 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

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OUTLINE

1. Introduction2. Processes and threads3. Deadlock4. Memory management5. Input/output6. File systems7. Multimedia operating systems8. Multiple processor systems9. Security

UNIX and Windows are to be used as running case studies.

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Introduction

Chapter 1

1.1 What is an operating system1.2 History of operating systems1.3 The operating system zoo1.4 Computer hardware review1.5 Operating system concepts1.6 System calls1.7 Operating system structure

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Introduction

• A computer system consists of– hardware– system programs– application programs

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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

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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

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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

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Second Generation (2)

• Structure of a typical FMS job – 2nd generation

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Third Generation

Third generation:• Multiprogramming • Timesharing• MULTICS => UNIX

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Fourth Generation

Fourth generation (1980- ) - Personal computers

• MS-DOS, • Graphical User Interface (GUI),• Windows,• Network and distributed OSs

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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

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Computer Hardware Review

• Components of a simple personal computer

Monitor

Bus

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Processors

(a) A three-stage pipeline(b) A superscalar CPU

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Memory

• Typical memory hierarchy– numbers shown are rough approximations

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Hard Disk

Structure of a disk drive

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Base-Limit Pairs

One base-limit pair and two base-limit pairs

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Interrupt

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

(a) (b)

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Pentium System

Structure of a large Pentium system

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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

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A Process Tree

A created two child processes, B and C

B created three child processes, D, E, and F

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Deadlock

(a) A potential deadlock. (b) An actual deadlock.

Read-write example

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Main Memory

Holds executing programs

Multiple programs - protection

Large programs - virtual memory

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File System

File system for a university department

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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

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Mounting

• Before mounting, – files on floppy are inaccessible

• After mounting floppy on b,– files on floppy are part of file hierarchy

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Pipe

Two processes connected by a pipe

e.g. sort <in|head -30

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System Calls

• Interface between OS and user programs (to perform privileged operations)

• Machine dependent, but procedure libraries

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Steps in Making a System Call

There are 11 steps in making the system call read (fd, buffer, nbytes)

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Some System Calls For Process Management

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Some System Calls For File Management

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Some System Calls For Directory Management

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Some System Calls For Miscellaneous Tasks

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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 */ }}

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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

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Mount

mount(/dev/fd0,/mnt,0)

(a) File system before the mount

(b) File system after the mount

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Windows System Calls

Some Win32 API calls

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Monolithic System

Simple structuring model for a monolithic system

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Layered System

Structure of the THE operating system

• MULTICS - concentric rings

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Virtual Machines

Structure of VM/370 with CMSCMS: Conversational Monitor System

VM: Virtual Machine Monitor - multiprogramming

• MS-DOS on Pentium

• JVM

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Exokernels

Similar to VM, but

• Restriction to allocated resources

• No need for remap

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Client-Server Model

Microkernel

• handles communication

• provides low-level resource management

Cf. Mechanism versus policy

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C-S Model in a DS

The client-server model in a distributed system