IO

• Character special files (or character devices or block-oriented device)

• Block special files (or block devices or block-oriented device)

• device file (or device node or special file)

  • major number 
  • minor number

• stream

  • bitstream (or bit stream or binary sequence)
  • bytestream

• parallel port

• serial port

• parallel communication

• serial communication

• data buffer (or buffer)

• control register

• Video random-access memory (VRAM)

• Memory-mapped I/O (MMIO)

• port-mapped I/O (PMIO)

• bus (historically also called a data highway or databus)

  • address bus
  • memory bus

• bus snooping (or bus sniffing)

• memory controller (or memory chip controller (MCC) or a memory controller unit (MCU))

• disk controller

• cycle stealing

• input–output memory management unit (IOMMU)

• buffer underrun (or buffer underflow)

• polling (or interrogation)

  • polled I/O (or software-driven I/O)

• Hot swapping

  • Hot plugging

• programmed input–output (or programmed I/O, PIO)

• interrupt-driven I/O

• Direct memory access (DMA)

  • registers:
    • byte count register
    • memory address register
    • control register(s), to specify:
      • I/O port to use
      • transfer direction (reading/writing)
      • transfer unit (byte/word at a time)
      • number of bytes to transfer in a burst
  • DMA controller

• reading from disk: (by (Tanenbaum, 2022))

  • (using interrupt-driven I/O)
    • disk controller:
      • read block (one or more sector(s)) (bit by bit)
      • store the block in its buffer
      • computes the checksum
      • causes an interrupt
    • OS:
      • reads the block from the disk controller buffer (using a loop where in each iteration it reads one byte/word from the register of the disk controller and writes it to the main memory)
  • (using DMA)
    • CPU:
      • programs the DMA controller (by writing to its registers)
      • instructs the disk controller to read data from the disk into the buffer of the disk controller and do the checksum verification
    • (when a verified data block is ready in the disk controller buffer then the DMA controller is triggered)
    • DMA controller:
      • issues a read request to the disk controller (via the bus)
    • disk controller:
      • transfers the data to the main memory (via the bus)
      • sends acknowledgment to the DMA controller (via the bus)
    • DMA controller:
      • sends an interrupt to the CPU when the entire block has been transferred

• Input/output (I/O) scheduling (or disk scheduling)

  • first-come, first-served (FCFS)
  • Shortest seek first (or shortest seek time first)
  • elevator algorithm (or SCAN)
  • circular SCAN (or C-SCAN)

References

• Tanenbaum, Andrew S. (2022). Modern Operating Systems. Pearson.