OPERATING SYSTEMS

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• OPERATING SYSTEMS

Lecturer Szabolcs Mikulas Office B38B E-mail
szabolcs_at_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
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• OUTLINE

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.
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Introduction

• Chapter 1

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
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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
Monitor
Bus

• Components of a simple personal computer

13
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)
(b)

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

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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

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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 CMS
• CMS 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