[Operating system] IO system concept

IO device classification

• By using the characteristics of the device
  • Storage devices
  • Input and output devices
  • Terminal Equipment
  • Offline device
• System point of view
  • According to data transfer rate
    • Low-speed devices
      • keyboard
    • Medium-speed devices
      • laser printer
    • High-speed devices
      • Disk drive
  • Press transmission (switching unit)
    • Character device
      • Bytes transmitted / characters belonging unstructured / slow devices
      • printer
      • Not addressable, the IO interrupt-driven, relatively low transmission rate
    • Block device
      • Typically as a storage device, a transmission units between the block size is 512B-4KB
      • Disk
      • Addressable, usually a DMA (direct memory access memory, direct access) mode
  • According to the shared property
    • The exclusive device
      • Only allows a period of time a user (process) access devices
      • Use: apply, use, use, ..., released
    • Shared Device
      • A period of time may allow more than one user (process) access devices
      • Use: use, use, use, ...
    • Virtual Device
      • Virtualization technology by the exclusive programming that can be shared logical device, available for multiple processes simultaneously access
      • -> spooling technology

Using a high-speed large-capacity devices can share the block (disk) to simulate the operation of the exclusive device, so that a plurality of devices into account independence can be used concurrently virtual device

Feature

• Increase speed IO
• The exclusive device instead shared device
• To achieve the function of the virtual device

IO control

• Direct control program
  • Direct control program (polling)
    • Without interruption mechanism
  • Interrupt control mode
    • Interrupt mechanism is introduced, CPU, and parallel device
  • DMA control
    • Open up a direct information channel between peripherals and memory
  • Control channel
    • A simple processor is simplified CPU (with its own instruction)

The main task of device management: control the data transfer between the device and memory / cpu

 

Buffering

• purpose
  • Matching CPU and peripheral speed
  • Reducing interrupt frequency
  • Improve the parallelism
• classification
  • Single buffer
  • Double buffering
  • Circular buffer
  • Buffer pool
• Buffer operation
  • Semaphore mechanism

Space for time, speed up data processing speed IO system