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Suppose any device which is connected at input-output port wants to transfer data to transfer data to memory, first of all it will send input-output port address and control signal, input-output read to input-output port, then it will send memory address and memory write signal to memory where data has to be transferred. In normal input-output technique the processor becomes busy in checking whether any input-output operation is completed or not for next input-output operation, therefore this technique is slow.
This problem of slow data transfer between input-output port and memory or between two memory is avoided by implementing Direct Memory Access DMA technique. Suppose a floppy drive which is connected at input-output port wants to transfer data to memory, the following steps are performed:. GeeksforGeeks has prepared a complete interview preparation course with premium videos, theory, practice problems, TA support and many more features.
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Direct memory access with DMA controller 8257/8237
For the execution of a computer program, it requires the synchronous working of more than one component of a computer. Usually, processors control all the process of transferring data, right from initiating the transfer to the storage of data at the destination. This adds load on the processor and most of the time it stays in the ideal state, thus decreasing the efficiency of the system. DMA controller transfers data with minimal intervention of the processor. The term DMA stands for direct memory access. The hardware device used for direct memory access is called the DMA controller.
Microprocessor - 8257 DMA Controller
Direct Memory Access (DMA) in Computer Architecture
It is designed by Intel to transfer data at the fastest rate. Then the microprocessor tri-states all the data bus, address bus, and control bus. These are the four individual channel DMA request inputs, which are used by the peripheral devices for using DMA services. When the fixed priority mode is selected, then DRQ 0 has the highest priority and DRQ 3 has the lowest priority among them.