Uncommon
Direct memory access
Feature of computer systems
Direct memory access
Direct memory access (DMA) is a feature of many computer systems that allows certain hardware subsystems to access main system memory independently of the central processing unit (CPU). Without DMA, programmed input–output must be used to transfer data which typically fully occupies the CPU for the entire duration of the transfer, and is thus unavailable to perform other work. With DMA, the CPU first initiates the transfer, then it does other operations while the transfer is in progress, and it finally receives an interrupt from the direct memory access controller (DMAC) when the operation is done. This feature is useful at any time that the CPU cannot keep up with the rate of data transfer, or when the CPU needs to perform work while waiting for a relatively slow data transfer. Many hardware systems use DMA, including disk drive controllers, graphics cards, network cards, sound cards and dedicated DMA controllers (acting on behalf of the aforementioned device types). DMA is also used for...
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