DMA

Direct memory access (DMA) channels are system pathways used by many devices to transfer information directly to and from memory. DMA channels are not nearly as "famous" as IRQs as system resources go. This is mostly for a good reason: there are fewer of them and they are used by many fewer devices, and hence they usually cause fewer problems with system setup. However, conflicts on DMA channels can cause very strange system problems and can be very difficult to diagnose. DMAs are used most commonly today by floppy disk drives, tape drives and sound cards.
A good example of Using Direct I/O with DMA you can find at:
http://www.osr.com/ddk/iputoput_0gx3.htm