A+ Hardware Service Technician: System Architecture

Previous Page - Next Page

DMA

DMA, or Direct Memory Access, is also a very important topic to study and understand. DMA channels allow devices to communicate directly with system memory without involving the CPU allowing for more efficient (faster) transfer of data. Newer PCs no longer require DMA, but older PCs may.

Hard drive controllers, NICs, and floppy disk controllers are three examples of devices that may use DMA in older systems.

In most PCs, there are 8 DMA channels (number 0 – 7). Channels 4-7 are generally available, while channel 0 is used to refresh DRAM, channel 1 is used by the hard disk controller or sound card, and channel 2 is used by the floppy disk controller.

Previous Page - Next Page