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DMA Controller and DMA Mode Support

Direct memory access (DMA) provides a way for devices to transfer information directly to and from memory, without the processor's intervention. This was originally conceived as a more efficient means of transferring information to and from memory than programmed I/O, as it allows the processor to do other work (when using an operating system that supports it). It is still used by many devices, although newer transfer modes are now used for high-performance devices like hard disks. DMA is controlled by the chipset's DMA controller, and the better (and newer) the controller, the more DMA modes its supports. See here for more details on DMA.

Bus mastering is an enhancement of DMA whereby the remote device not only can send data to the memory directly, it actually takes control of the bus, and performs the transfer itself instead of using the DMA controller. This cuts down on the overhead of having the (relatively slow) DMA controller talk to the device doing the transfer, further improving performance. Bus mastering support is also provided by the chipset.

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