I/O Devices

• Categories of I/O Devices (by usage)
  • Human readable
    • Used to communicate with the user
    • Printers, Video Display, Keyboard, Mouse
  • Machine readable
    • Used to communicate with electronic equipment
    • Disk and tape drives, Sensors, Controllers, Actuators
  • Communication

    Figure 5: A kernel I/O structure.

    
    • Used to communicate with remote devices
    • Ethernet, Modems, Wireless
• I/O system calls abstract device behaviors in generic classes (see Fig. 5)
• Device-driver layer hides I/O-controller differences from kernel
• Devices vary in many dimensions
  • character-stream or block
  • sequential or random-access
  • sharable or dedicated
  • speed of operation
  • read-write, read only, or write only
• Block and Character Devices; Block devices include disk drive
  • commands include read, write, seek
  • raw I/O or file-system access
  • file system maps location i onto block + offset
  • memory-mapped file access possible
• Character devices include keyboard, mouse, serial port
  • commands include get, put
  • libraries layered on top allow line editing