24308 CSC 080A - 0 - Operating Systems Spring 2003 Monday, 5:30 pm - 8:10 pm , Kramer Science Center 102A Herbert J. Bernstein (yaya@dowling.edu) Introduction

This web page is http://www.bernstein-plus-sons.com/.dowling/CSC080/CSC080_Introduction.html
Copyright © 2001, 2002 Herbert J. Bernstein and other parties. All rights reserved.

Introduction to Operating Systems

• Introduction to Professional Issues:
  • ethical issues;
  • fiduciary responsibility
  • systems mindset; service mentality proactive approach; Murphy's Law; KISS
• Introduction to Systems Programming
  • software engineering in the context of operating systems
    • review of top-down analysis, bottom-up synthesis, object-oriented analysis
    • missing top, rigid bottom, naturally object-oriented
    • outside-in programming, multiple goals, multiple resources
  • understanding how devices are managed
    • representation of information by changes in physical state
      • contact closures
      • magnetization
      • optical properties
    • map from physical to logical states
      • interfaces
      • controllers
    • device drivers
      • buffering time
      • polling
      • interrupts
    • application interfaces
      • buffering data
      • circular buffers
• Role and Purpose of Operating Systems

  Different application programs written for use on computers are likely to have common needs, especially if multiple applications will share resources on the same computer. Resources can be managed effectively and programming effort conserved if a systematic approch is taken to providing support services to applications. "Operating Systems" have been created to allocated shared resources in a systematic manner. In addition, many applications which support the creation and management of user applications are handled as an aspect of systems programming. For example, compilers and their associated libraries are considered systems software.

  • Manage shared resources
  • Create virtual resources (extend the basic hardware)

• Partial History

  Time Period	Resource Management Approach
  1930's, 1940's, early 1950's	Private, serial use of computers, resources scheduled on paper: sign-up sheets
  Mid 1950's	Software-managed serial use of computers, users replaced by computer operators, creation of batch monitor systems, GE/NAA I/O System 1955 first consideration of "time-sharing".
  Early 1960's	batch monitor systems become batch operating systems FMS (Fortran Monitor System) 1960, SOS (Share Operating System) 1960, became IBSYS first time-sharing operating system (MIT CTSS) 1961
  Mid 1960's	multi-programmed batch operating systems CDC-6600 Chippewa Operating System, OS/360 Multics, virtual machines, 360/67 and CP/CMS DEC PDP-6 1964, DEC PDP-10, PDP-8
  Late 1960's	time sharing and multiprogramming mature, "permanent" files develop, first Unix designs.
  1970's	Commercial and academic time-sharing on DEC PDP10's using TOPS-10, Arpanet 1970, PDP-11 (http://telnet.hu/hamster/pdp-11/main.html) 1970, DOS/BATCH, RT-11, RSX-11, ... (http://www.village.org/pdp11/faq.pages/pdpOSes.html) VAX 1977, VMS 1978 CP/M 1973 (http://www.armory.com/~spectre/tech.html) Xerox Alto 1972 (http://members.fortunecity.com/pcmuseum/alto.html)

  Many operating systems were developed. At present the major threads of development have converged on the various Unix descendents, various "Mainframe" operating systems, and various PC operating systems. Many of the GUI concepts now used come from work at Xerox PARC in the mid 1970's (see http://members.fortunecity.com/pcmuseum/alto.html), and were brought to commerical success via the Apple Macintosh Operating System in 1984. Except for Microsoft Windows, most platforms seem to be converging onto Unix variants, and Microsoft Windows makes use of many features from Unix operating systems.

• Major Operating System Functions
  • Allocation of resources
    • CPU
    • memory
    • disk space, file systems
    • network access
  • Protection of resources
  • Accounting of resources
  • Problem detection and resolution
  • Optimize utilization
  • Optimize performance
  • Provision of useful facilities
    • device drivers
    • API's
    • languages
    • libraries
    • GUI interfaces
• Major Operating System Types and Features
  • Batch -- processing of a pool of applications
  • Timesharing -- create the illusion of multiple computers by switching rapidly among applications or users
  • Multiprogramming or multitasking -- multiple programs or tasks progress "simultaneously"
  • Multiprocessing -- managing multiple CPU's within one system with load sharing
  • Multiuser -- supporting the work of multiple users, often with "private" virtual machines
  • Realtime -- able to interact with external events and processes without significant delay
  • Mobile -- with features to support portable computers
  • GUI -- providing a graphical user interface
  • Command line -- managed by typed command lines
• Threads, interrupts and multi-tasking
  • Single thread model: -- OS services requests from applications one at a time, to completion
  • Single thread with interrupts: -- Real time demands serviced by interruping main thread of execution, saving state, doing urgent task, restoring state, and resuming original thread.
  • Multiple threads: -- Multiple independent tasks progress independently, may be non-preemptive (on I/O interrupts only) or preemptive clock-driven round robin.
• Unix
  • Developed at Bell Labs in the early 1970's
  • System kernel provides well-defined interface to hardware
    • System call interface
    • File subsystem
      • device drivers
    • Process control subsystem
  • Kernel wrapped in one or more shells
  • Multitasking, multiuser systems with full protection and multiprocessor support
  • Round robin preemptive multi-threading
  • Extensive open-source support
  • Newer versions allow modular, dynamic loading of major system components (loadable modules)

• MS Windows
  • Based on MS-DOS, derived from CP/M
  • GUI interface introduced with Windows 1.0 in 1985
  • Windows NT, 95, etc. started the break with DOS
  • See http://www.computerhope.com/history/windows.htm and http://members.fortunecity.com/pcmuseum/windows.htm for a history of MS Windows.
  • Designed to support a wide range of "legacy" applications.
  • Modern versions, primarily single-user, multi-tasking systems
  • Increasingly unix-like premeptive process scheduling
  • Server versions provide services for multiple users of some subsystems (file services, web services).

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  Prepared 9 December 2001,
  Updated 3 March 2003
  yaya@dowling.edu.