DMA

(də¦rekt ¦mem·rē ′ak′ses)

(computer science) The use of special hardware for direct transfer of data to or from memory to minimize the interruptions caused by program-controlled data transfers. Abbreviated dma.

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(1) (Digital Media Adapter) See digital media hub.

(2) (Document Management Alliance) A specification that provides a common interface for accessing and searching document databases. It provides interoperability between multivendor document management systems. DMA was released in 1998 by the DMA task group of the AIIM association. See AIIM.

(3) (Direct Memory Access) Specialized circuitry or a dedicated microprocessor that transfers data from memory to memory without using the CPU. Although DMA may periodically steal cycles from the CPU, data are transferred much faster than using the CPU for every byte of transfer. On PCs, there are eight DMA channels commonly used as follows. Most sound cards are set to use DMA channel 1. See PIO mode.

   DMA    Used for
   0      8-bit transfer
   1      8-bit transfer
   2      Floppy disk controller
   3      8-bit transfer
   4      Cascaded from 0-3
   5      16-bit transfer
   6      16-bit transfer
   7      16-bit transfer

DMA Disk Transfers

There are various modes of data transfer on IDE disk drives. The PIO modes use the CPU, and the DMA modes bypass the CPU.

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