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I/O System

1017.pngI/O management is a major component of operating system design and operation

  • Important aspect of computer operation
  • I/O devices vary greatly
  • Various methods to control them
  • Performance management
  • New types of devices frequent
  • Ports, busses, device controllers connect to various devices

Direct Memory Access

1023.pngUsed to avoid programmed I/O (one byte at a time) for large data movement

1028.pngRequires DMA controller

1033.pngBypasses CPU to transfer data directly between I/O device and memory

1038.pngOS writes DMA command block into memory

  • Source and destination addresses
  • Read or write mode
  • Count of bytes
  • Writes location of command block to DMA controller
  • Bus mastering of DMA controller - grabs bus from CPU
  • Cycle stealing from CPU but still much more efficient
  • When done, interrupts to signal completion
  • Version that is aware of virtual addresses can be even more efficient - DVMA


Interrupt-Driven I/O Cycle

Six Step Process to Perform DMA Transfer



Characteristics of I/O Devices


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