Overview of OS

• What’s an OS?

  • Extended machine (abstraction layer)
  • Resource Manager

• Process

  • A program in execution (aka job or task)
  • Has CPU state, or context, in registers
  • Has allocated resources
    • PCB = Process Control Block
    • Memory
    • Files, network resources

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• Process States
  • Running
  • Blocked or wait or suspended
  • Ready
• I/O Methods
  • Programmed I/O (device driver), write date to device data register, setup other registers, and wait.
  • Interrupt driven I/O
  • DMA I/O (Direct Memory Access)
    • Interrupts are served by DMA
    • In traditional interrupt driver IO, data are first copied to OS memory space.

OS Architecture

• Layered OS
  • Not as efficient - errors may need to pass through many layers to go down to hardware
• Monolithic
  • OS composed of a single module
  • All data and code use same memory space
  • Low overheads and easy to implement
• Microkernel
  • Remove as much functionality from OS as possible
  • Security and protection can be enhanced
  • System expansion can be easier
• Hybrid
• Distributed