Operating Systems AMS505 4'3 Winter 2001

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Operating SystemsAMS505 4.3 Winter 2001

• Major Greg Phillips
• Royal Military College of Canada
• Electrical and Computer Engineering
• greg.phillips_at_rmc.ca
• 1-613-541-6000 ext. 6190

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AMS 505 Road Map

• 2. Hardware
• physical aspects of how computers work
• 3. Networks
• how computers communicate with one another
• 4. Software
• how we give the hardware behaviour
• 5. Databases
• how we organize, store, and retrieve information
• 6. IS Development
• issues in getting information systems built
• 7. Information Security
• keeping our information secret, correct, and
  available
• 8. Applications
• selected military-relevant application areas

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Software Module

• 4.1 the software hardware interface
• plus lab 4.2
• 4.3 operating systems and higher-level
  programming models
• 4.4 procedural programming
• plus lab 4.5 using Python
• 4.6 object-oriented programming
• plus lab 4.7 using Python
• 4.8 parallel and distributed systems

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Today

• historical overview of operating system
  development
• what they are, and where they came from
• programming models
• how programs run on our machines
• key operating system features and services
• what they do, and how

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In the beginning, there was The Machine.
And it was alone.
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Time of the Disciples (c. 1945-1955)
Programming from the console (A Disciple communes
with The Machine).
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Time of the Disciples

• one user, one computer
• programs entered directly on system console
• inefficient use of machine time
• occasionally, paper tape substituted
• programs written in machine language or possibly
  assembler
• error-prone, requires many steps to perform any
  useful computation
• programs written at machine hardware level
• special programs required for each device or
  peripheral
• rewrite any time one of these changes

hand-coded program
hardware
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The High Church (c. 1950-1982)
Punching cards (Monks prepare the Sacred Text).
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The High Church
Entering a job (An Acolyte presents the Sacred
Text to The Machine).
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The High Church

• many users, one computer (one at a time)
• programs punched on cards, then submitted to
  machine room for processing output returned on
  printouts
• more efficient use of expensive machine time
• programs written in higher-level languages
• easier to write correct programs, detect errors,
  maintain programs over time
• early operating systems provide hardware
  abstraction
• program to generic device model OS takes care of
  translation
• change of device requires OS device driver
  update only
• e.g., ADMIRAL, IBM 1410 OS, SABRE

compiler
compiled program
program source
hardware abstraction layer
operating system Application Programming
Interface (API)
hardware
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First Reformation (c. 1965 - now)
Timesharing systems (The People speak to The
Machine, from afar).
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First Reformation

• many users, one computer (time sharing)
• programs entered directly on teletype machines or
  dumb terminals and stored on disk or tape
• efficient use of expensive machine time, but more
  effective for users
• early time-sharing OS allow multiple, parallel
  users
• arbitration of shared resources
• CPU time, memory, tape and disk, printers
• provision of essential system services
• command shells, etc
• e.g., TSS, TOPS-10, Multics, VMS, Unix

compiled program
compiled program
compiled program
time-sharing operating system
hardware
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Second Reformation (1969 - now)
Personal computers (The People commune with Their
Machines).
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The Second Reformation

• one user, one or more computer (personal
  computers)
• machine time is cheap, put them everywhere!
• programs entered directly into computers, stored
  on disk
• although hardly anyone actually programs any
  more
• typically single user OS, but have multiple
  active processes (still many multi-user OS)
• arbitration of shared resources still an issue
• provision of useful higher-level services
• graphical user interface components, window
  managers, file system explorers, help systems,
  configuration utilities, automatic device
  detection (plug and play), install and
  uninstall utilities,
• e.g., Windows, MacOS, Linux, PalmOS, etc.

compiled program
compiled program
compiled program
time-sharing operating system
hardware
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Key OS Features and Services

• process management
• allowing multiple programs to run on one machine
• memory management
• giving each process access to independent memory
• storage abstraction
• allowing a consistent interface to different
  kinds of secondary storage
• security management
• supporting privacy, integrity, availability

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Process management

• on modern OS, many active processes
• system level housekeeping
• background daemons
• event schedulers, print/web/ftp servers
• user applications
• process has
• own program counter or thread of control
• protected region of memory
• OS provides process scheduling
• which process is active when
• typically performs context switch every few
  milliseconds
• provides illusion that each program runs
  continuously

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Memory management

• with multiple processes in memory, must ensure
  one process doesnt overwrite anthers program or
  data
• key concept virtual address space
• from programmer/process perspective, appears
  process has continuous access to full machine
  address space
• OS (hardware) actually maps program virtual
  addresses to machine addresses
• mapping ensures each process has protected space
• side benefit virtual memory
• can map program addresses to disk pages
• allows processes to use more physical memory
  (RAM) than machine actually contains
• but RAM 106 times faster than disk

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Storage abstraction

• lots of different physical storage mechanims
• floppy, hard disk, CD-ROM, flash memory, tape
• OS provides common abstraction of files
• file appears to be a continuous stream of any
  number of bytes
• typically really stored in fixed-size blocks,
  scattered across a disk or tape
• and directories
• looks like a container full of files
• really just a special file listing the files it
  contains
• OS API for files
• open(), close(), read(), write(), seek()
• and directories
• change_directory(), list_contents(), add(),
  remove()

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Security Management

• virtual address space is a security mechanism
• typically want to authenticate users and provide
  distinct privileges to each login password
• must protect files if multiple users
• MacOS, Windows 9x, PalmOS
• no concept of file ownership
• Unix, Linux, MacOS X (based on BSD Unix)
• files have owners and groups
• for owners, groups and others can set separate
  permissions for reading, writing, and executing
  files
• Windows NT/2000
• files have owners
• can assign permissions to individual users or
  groups (access control list) read, write,
  execute, delete, change permissions, take
  ownership

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Join the RMC or Queens Jugglers!

• RMC (New Gym)
• Tuesday evenings, 2130-2300 hrs
• Queens (Biosciences Atrium)
• Tuesday evenings, 1900-2100 hrs
• Saturday afternoons, 1400-1600 hrs (not 27 Jan
  01)
• http//www.ams.queensu.ca/juggling/