Direct memory access

Direct Memory Access (DMA for short). DMA allows certain hardware (say, Hard Disk Controller, Disk Drive Controller, Graphics Card or Soundcard) to access system memory for reading and/or writing independently of main CPU.

DMA is an essential feature of all modern computers, as it allows devices of different speeds to communicate without subjecting the CPU to a massive interrupt load.

"Scatter-gather" DMA allows the transfer of data to multiple memory areas in a single DMA transaction. It is equivalent to the chaining together of multiple simple DMA requests. Again, the motivation is to off-load multiple I/O interrupt and data copy tasks from the CPU.