Write on short note DMA.

Direct Memory Access (DMA) is a technique for transferring data from  main to a device without passing it through the CPU. Computers that have DMA channels are able to transfer data to and from devices much more quickly than computers without a DMA channel can. This is helpful for making quick backups and for real-time applications.

A few expansion boards such as CD-ROM cards are capable of accessing the computer's DMA channel. When you install the board, you should specify which DMA channel is to be used, which sometimes engross setting a jumper or DIP switch.