Operating Systems Lecture Notes

23 January 2012 • Operating Systems

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Outline

• What is an operating system?
• For whom does the OS toil?
• Requirements and trade-offs.
• History
• Developments

What Is An Operating System?

What Is An Operating System?

• It’s a program; a big piece of software.

  Normally, operating systems run directly on hardware.

  More recently, it may run on other software.

Operating System Function

• An operating system creates and manages resources.
• “Manages” means both exploit (maximize good use) and protect (minimize bad use).
  • Good uses includes cooperation and sharing.
  • Bad use includes
    • disruption, as in resource hogging, and
    • disrespect, as in illicitly accessing information.

Resources

• Resources are practically everything, including programs, including the OS.
• An OS creates resources by
  • adapting hardware resources (CPU, disk), or
  • synthesizing resources (network connections, file locks).

For Whom does the OS Toil?

• An OS provides these resources for programs executing on the system.
  • Process: a program executing on the system.
  • Processes are a resource synthesized by the OS.
• By extension, and indirectly, the OS provides resources for the process’s clients.
  • Client: whatever executes a program.
  • Clients needn’t be human.

OS Requirements

• Three OS requirements: economy, protection, and convenience.
• Economy: efficiently manage resources; expensive (user time) or limited (handheld power) or both (wireless transmission bandwidth).
• Protection: prevent various levels of malevolent or inadvertent resource abuse.
• Convenience: present resources at the right level of detail (abstraction).

Trade-Offs

• The requirements are in conflict:
  • Economy vs convenience
  • Convenience vs protection
  • Protection vs economy
• There are other requirements (generality, accountability).
  • And conflicts (scope, cost).
• Economy > convenience > protection, traditionally.

Trade-Offs Illustrated

• Trade-offs are knobs in the OS design space.
  • Each settings group is a different OS.

OS Techniques

• An OS does its work by implementing abstractions.
• An abstraction is a high-level model defined in terms of low-level details.
  • The high-level models is more convenient to use than the low-level details.
  • However, it may not be as efficient, or as flexible.

OS History

• OS development responds to technological and development forces.
  • Technological forces are more or less straight line.
  • Development forces are cyclical and more or less eternal.
• OS characteristics wax and wane with these forces, but never disappear.

Pre ’60s

Pre ’60s OSs

• Environment
  • Limited, expensive, strange machines.
• Requirements
  • Produce results to justify costs.
• OSs
  • A collection of common libraries.
• Computers were accepted as valuable tools.

The ’60s

’60s OSs

• Environment
  • Big expensive machines; IBM 360, CDC 6600.
• Requirements
  • Maximize investment and manage complexity.
• OSs
  • Batch operating systems: OS/360.

The ’70s

’70s OSs

• Environment
  • Big, expensive machines: PDP 10.
• Requirements
  • Reduce support personnel, improve programmer interactions.
• OSs
  • Timesharing operating systems provided the virtual machine abstraction.

The ’80s

’80s OSs

• Environment
  • Small expensive machines: PDP 11.
• Requirements
  • Reduce complexity, improve problem throughput.
• OSs
  • Specialized operating systems: RTOS.

The ’90s

’90s OSs

• Environment
  • Small, cheap machines; IBM PC.
• Requirements
  • Simplicity, minimal training.
• OSs
  • Single-user operating systems; Windows, Oberon, NeXTSTEP

The ’90s

’00s OSs

• Environment
  • A Cambrian explosion; networks, hand-helds.
• Requirements
  • Manage severely constrained or ad hoc resources.
• OSs
  • Symbian, BeOS, TinyOS.

Why Bother?

• Aren’t operating systems a done deal?
• Operating systems evolve in response to changing environments.
  • Hardware: networked machines, 64-bit address spaces, mobile and other low-resource environments.
  • Resources: information and rights management.
  • Requirements: security, ambient computation.

Automotive Electronics

• Consider automotive electronics.
  • Chassis control, engine control, automatic transmission ABS/ASR, cruise control.
  • Cabin comfort, air conditioning, dashboard, trip computer, display range, radio, telephone, navigation.
  • Intelligent switching, anti-finger traps, power seats, alarms.
• Remember: your break pedal is an input device.

Automotive CPUs

• These applications require dozens of CPUs.
  • 32-bit power train, 16-bit vehicle control, 8-bit body control and driver information, 4-bit dashboard.
• Now, network them together, multiplex them, link them up to the external environment.

Sensor Networks

• How would you do constant Leach's storm petrel surveys?
• How would you study the forest ecology of wild fires?
• Have lots of small, cheap sensors scattered around.
  • Each sensor is self contained and long lasting.
  • Individual sensors coordinate without leaders.

Sensor Networks OSs

• Operating systems for sensor networks
  • Have access to limited facilities.
  • Manage scarce and expensive resources, power particularly.
  • Orient towards a particular application.
  • Deal meaningfully with uncertain environments.
• Examples: TinyOS, LiteOS, SOS.

Summary

• An operating system is a resource manager.
  • It's also responsible for creating the resources managed.
• OSs respond to influence from the environment and requirements.
  • There'll always be a need for new OSs, or better versions of existing OSs.
• Old OS ideas never die, they're resurrected in slightly different form.

Credits

• L’Aquàrium: Octopus by Sebastian Niedlich under a Creative Commons BY NC SA license.
• UNIVAC I Mercury Delay Line by Austin Appel under a Creative Commons BY NC SA license.
• IBM System 360 by Michael Cote under a Creative Commons BY license.
• PDP 10 by Michael Umbricht under a Creative Commons BY SA license.
• from archive: lucifer by Harri Haataja under a Creative Commons BY NC SA license.
• 66 Mhz of x86 Power by Miles Bannan under a Creative Commons BY SA license.
• Amazing Blackberry by Ninja M. under a Creative Commons BY NC SA license.

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This page last modified on 2012 February 14.