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direct memory access

direct memory access (DMA) A method whereby I/O processes can obtain access to the CPU's memory while a program is running. This is accomplished by permitting the I/O controller or channel that has been previously instructed to move a block of data to or from the memory to temporarily take control of the memory for (usually) one memory cycle by specifying the memory address, thus allowing a single word (or group of words if the memory is so organized) to be read or written. The method is therefore also referred to as cycle stealing. The timing requirement is normally that of the slower external device and is prompted by the ability of that device to receive or provide desired data, hence the alternative synonym data break.

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