I / O devices – geeksforjobs


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  • Internal communication between the I / O devices and the processor and main memory is done by the bus.
  • A bus is a group of wires that are used to connect the internal components of a computer.
  • Example: The user is typing something using a keyboard which is an input unit. The connection is established such that the input is transferred to the processor via the bus and then stored in the main memory which data is captured from the main memory via the bus to the I / O devices.
  • Bus
    • Address Lines -> Data Address
    • Data line -> data stored in data lines
    • Control Lines -> Control Bus Activity

Direct Memory Access (DMA)

INPUT ——> PROCESSOR ——-> main memory ——-> OUTPUT


  • In each action, the processor is involved in data transfer and takes more computing time to complete the process.
  • Processor is mandatory in every computer system. The DMA module is a hardware module that is used in place of the processor.
  • The input is moved to the DMA controller and then to the main memory and then to the output.
  • Data transfer occurs without the inclusion of the processor so it is direct memory access.
  • The DMA controller works faster than the processor.
  • If the DMA wants to store data then it stores the data in the disk.

Bus arbitration

Device 1 ______________________ communication ______________________________ device 2

  • The communication should be via the bus then anyone on the device should initiate a transfer.
  • If device 1 starts communication then it is called bus master.
  • Bus arbitration is a process of selecting a bus master based on capabilities.

Bus arbitration method

  1. Centralized arbitral award : Most systems use it. Centrally the processor decides the transfer so it is called centralized arbitration.

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