What is DMA? Why does the DMA generally have priority over the CPU in the case of accessing memory?

Subject Peripheral and Interfacing
NU Year Set: 2.(a) Marks: 4 Year: 2017

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).

We can transfer data direct to and from memory without the need of the CPU. The transfer of data between a fast storage device such as magnetic disk and memory is often limited by the speed of the CPU. Removing the CPU from the path and letting the peripheral device manager the memory buses directly would improve the speed of transfer. This transfer technique is called Direct memory access(DMA).
During DMA transfer, the CPU is idle and has no control of the memory buses. A DMA controller takes over the buses to manage the transfer directly between the I/O device and memory.


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