Question

Describe DMA and its actions. Why is DMA controller access to main memory in most systems given higher priority than a CPU access to main memory?

Answer 1

First Part:

DMA stands for direct memory access. This can be defined as a technique where hardware components can access main memory (RAM) without any dependency of CPU.

The transfer speed between two memory devices like magnetic disk and RAM is dependent on the CPU speed. In DMA mode the CPU does not involve in the transfer process and the peripheral device manager manages the memory bus. This process speed up the data transfer.

Second Part:

DMA controller access has a higher priority than the CPU access. In DMA mode the CPU has no control over the memory buses. The DMA controller controls the memory buses and controls the transfer between the I/O device and the memory. When the CPU detects a DMA mode operation, it does not interfere in the process and stay idle while waiting for the confirmation that the memory transfer is completed.

Hope this helps.