When programmed IO is suitable than other IO handling techniques? Explain the process of IO handling using DMA.

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Suresh Chand · Accepted Answer

Programmed IO is more suitable than other IO handling techniques when the CPU is not busy in other higher priority tasks and it can check each I/O device in sequence and in effect 'ask' each one of them if it needs communication with the processor. It is suitable when no interrupt hardware support is required. Direct memory access (DMA) is a method that allows an input/output (I/O) device to send or receive data directly to or from the main memory, bypassing the CPU to speed up memory operations. The process is managed by a chip known as a DMA controller (DMAC). The unit communicates with the CPU through the data bus and control lines. Through the use of the address bus and allowing the DMA and RS register to select inputs, the register within the DMA is chosen by the CPU. RD and WR are two-way inputs. When BG (bus grant) input is 0, the CPU can communicate with DMA registers. When BG (bus grant) input is 1, the CPU has relinquished the buses and DMA can communicate directly with the memory. The CPU initializes the DMA by sending the given information through the data bus. The starting address of the memory block where the data is available (to read) or where data are to be stored (to write). It also sends word count which is the number of words in the memory block to be read or written. Control to define the mode of transfer such as read or write. A control to begin the DMA transfer.

When programmed IO is suitable than other IO handling techniques? Explain the process of IO handling using DMA.

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When programmed IO is suitable than other IO handling techniques? Explain the process of IO handling using DMA.

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