Chapter 4: What is an operating system

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Chapter 4 What is an operating system?
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What is an operating system?

• A program or collection of programs that
  coordinate computer usage among users and handle
  common tasks.

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OS - functions

• Hide details of input and output
• Provide an environment for multiple
  users/programs to work concurrently
  multitasking and multi-slacking
• Allocate memory to different users/programs
• Share resources (files, printer) among users
• Provide means for users/programs to communicate
  with each other
• Provide protection and security for programs

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OS functions - examples

• You can access disks as file cabinets without the
  knowledge of tracks, sector, etc hide I/O
  details
• You can work with multiple programs at the same
  time, e.g., using IE to download files and use
  Word to write a report - multitasking
• In STT475 and 375, we share the same printers
  share resources
• You can interact with machines via the Internet
  communicate among users/machines
• When you use password on your machine, no one can
  use your computer without the password -
  protection

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Why are there difference OSs?

• Different types of cars for different purposes
• Vans for family
• Compact cars for gas mileage
• SUV for rough terrains
• Different OSs for different environments and
  applications
• Windows 2000/XP for personal computers
• Windows 2003 Servers for web servers and big
  corporations
• Unix/Linux for personal computers and servers

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What is multitasking?

• The speed of CPUs is much faster than any I/O
  device
• If a computer only execute one program (e.g.,
  Word) from beginning to end, the CPU would stay
  idle most the time since no human can type fast
  enough.
• Multitasking allows multiple programs to reside
  in the memory/virtual memory at the same time and
  switch the CPU between those programs

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Why OSs need to coordinate programs?

• Printing example
• When you print a Word document and a webpage at
  the same time on your home printer, did you ever
  find that one is printed in mid of the other?
• The OS determines which program uses the printer
  first and then next program
• Memory example
• When you use Word and IE at the same time, the OS
  must allocate memory space for both programs

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What is booting?

• Start up the computer and allow the OS to set up
  itself
• Then the OS starts behind-the-scenes programs
  (services) for special tasks
• Monitoring email, coordinating printing requests,
  monitoring data on the network.

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What cant Windows read Mac or Linux disks

• Different OSs define tracks and sectors
  differently on the disk formatting
• Windows machines do not know how to interpret
  Macs format
• Today, Mac machines can read Windows disks is
  because that Mac OS tries to read disks in
  Windows format after it fails to read it in Macs
  format.

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Portable storage devices

• Floppy disks
• Limited capacity, very slow, not reliable
• Most of todays PCs do not even install floppy
  disk drives
• Jumpdrive, pin drive, USB memory stick, flash
  memory, etc
• High capacity, fast, and reliable
• Use USB connection

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What is reboot?

• Stop all current processing and
• Restart the computer
• If everything were perfect in a computer, reboot
  would not be needed
• Reboot sometime is the most efficient way to
  restore the computer back to normal
• Reboot is the only way to restore the system when
  the computer does not respond to any keystroke
  and mouse

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Which OS is best?

• Three most common OSs
• Windows by Microsoft
• Aggressively marketed
• Take a large fraction of individual stations
• As a result, users can easily share programs and
  data
• Macintosh OS X by Apple
• Offers a simple, clean, and powerful graphical
  user interface
• Linux by Linus Torvalds and others
• Offer higher reliability and ability to link
  complex tasks

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Summary chapter 4

• Operating systems handle common tasks
• Identify one user from another
• Scheduling and coordinating processing
• Allocating resources (RAM, CPU time, printer,
  etc) to programs
• Multitasking allows a computer to split its CPU
  time and resources among multiple programs and
  users
• Booting restarts the computer and the OS sets up
  the environment
• Rebooting involves shutting down the computer and
  starting it up again
• Different OSs are designed for different
  purposes
• Different OSs define different formats on disks

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Terminology

• Operating systems
• Booting a computer
• Rebooting a computer
• Single-tasking
• Multitasking

• MS Windows
• Mac OS X
• Linux