COP 4610

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COP 4610

• Introduction to Operating Systems

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Chapter 1 - Introduction

• OS - Layer between the hardware and user programs
  (Figure 1.1)
• OS - The ultimate API
• OS - First program that runs when the computer
  boots up
• OS - Program that is always running
• OS - Typically only one instance/machine

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• An OS functions as a resource manager and an
  implementer of virtual computers
• As a resource manager, the OS handles hardware,
  typically consisting of
• Processor
• Memory
• I/O controllers
• Disk devices
• Other I/O devices
• Abstract H/W diagram Figure 1.2

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• Resource management by an OS involves
• Transforming a physical resource into an instance
  of a virtual resource (e.g., a printer)
• Multiplexing between different instances of a
  virtual resource when theres only one physical
  resource (e.g., use of SPOOLing disk files for
  virtual printers)
• TDM (time division multiplexing) vs SDM (space
  division multiplexing) some resources make sense
  to TDM (printer) others SDM (disk)
• Scheduling resources between programs

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• An OS creates a virtual computer for each
  program, with each its own
• Process(es) (TDM)
• Address space(s) (SDM)
• Disk objects/file system (SDM)
• The illusion is complete Figure 1.3
• Each virtual component has its own rules
• Figure 1.4 Virtual Processor
• Some native real processor instructions are
  masked new instructions are added (aka system
  calls)
• Pvirtual Pphysical - Priv. Instr Useful
  Instr

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• Each virtual component has its own rules
• Figure 1.4 Virtual Processor (continued)
• Separation of instruction privileges decided
  (hopefully!) by hardware states system and user
• Protected instructions are those which allow
  indiscriminate access to the hardware (address
  all of memory, access any I/O device, etc.)
• Figure 1.5 Virtual Primary Memory
• Create illusion that each program has its own
  private memory starting at address 0
• Figure 1.6 Virtual I/O
• Create illusion that each program has its own
  set of hardware devices

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• Figure 1.7Virtual Secondary Memory
• Create illusion each program has its own private
  disk drive/file system