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DMA

DMA. allows certain hardware subsystems within the computer to access system mem. independently of the CPU. Many hardware systems use DMA including disk drive controllers, graphics cards , network cards , and sound cards .

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DMA

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  1. Rachel Jiang, 2007 DMA • allows certain hardware subsystems within the computer to access system mem. independently of the CPU. Many hardware systems use DMA including disk drive controllers, graphics cards, network cards, and sound cards. • have DMA channels can transfer data to and from devices with much less CPU overhead than without a DMA channel. • DMA transfers are essential to high performance systems.

  2. Rachel Jiang, 2007 DMA • Without DMA, the CPU typically has to be occupied for the entire time it's performing a transfer. • With DMA, the CPU would initiate the transfer, do other operations while the transfer is in progress, and receive an interrupt from the DMA controller once the operation has been done

  3. Rachel Jiang, 2007 NO DMA • slower than copying normal blocks of memory since access to I/O devices over a peripheral bus is generally slower than normal system RAM. During this time the CPU would be unavailable for any other tasks involving CPU bus access, although it could continue doing any work which did not require bus access.

  4. Rachel Jiang, 2007 DMA Flowchart for a Disk Transfer

  5. Rachel Jiang, 2007 DMA Transfer from Disk to Memory Bypasses the CPU

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