DMA

Direct Memory Access (DMA)
Definition: A direct memory access (DMA) is an operation in which data is copied (transported) from one resource to another resource in a computer system without the involvement of the CPU.
Direct Memory Access is a capability provided by some computer bus architectures that allows data to be sent directly from an attached device (such as a disk drive) to the memory on the computer s motherboard. The microprocessor is freed from involvement with the data transfer, thus speeding up overall computer operation.
An alternative to DMA is the Programmed Input/output (PIO) interface in which all data transmitted between devices goes through the processor.
Fig(1) Computer system with DMA
Note//BG: bus grant signal and BR: bus ready signal
Advantages of DMA
-Fast memory transfer of data
-CPU and DMA run concurrently under cache mode
-DMA can trigger an interrupt, which frees the CPU from polling the channel
Use of this mechanism can greatly increase throughput to and from a device.
University of Babylon/College of IT S/W Dept. 3rd Class/Computer Architecture