INPUT OUTPUT ARCHITECTURE (PART III)

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8. INPUT OUTPUT CHANNELS AND PROCESSOR

1. Processor directly controls peripheral device
2. Addition of a controller or I/O module – programmed I/O
3. Same as 2 – interrupts added
4. I/O module direct access to memory using DMA
5. I/O module enhanced to become processor like – I/O channel
6. I/O module has local memory of its own – computer like – I/O processor
• More and more the I/O function is performed without processor involvement.
• The processor is increasingly relieved of I/O related tasks – improved performance


Characteristics of Input Output Channels

• Extension of the DMA concept
• Ability to execute I/O instructions – special-purpose processor on I/O channel –
complete control over I/O operations
• Processor does not execute I/O instructions itself – processor initiates I/O
transfer by instructing the I/O channel to execute a program in memory
• Program specifies
        - Device or devices
        - Area or areas of memory
        - Priority
        - Error condition actions

Type of Input Output Channels

• Selector channel
        - Controls multiple high-speed devices
        - Dedicated to the transfer of data with one of the devices
        - Each device handled by a controller, or I/O module
        - I/O channel controls these I/O controllers
• Multiplexor channel
        - Can handle multiple devices at the same time
        - Byte multiplexor – used for low-speed devices
        - Block multiplexor – interleaves blocks of data from several devices.

nadhiah amira nordin

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