Direct Memory Access (DMA) is a capability provided by some computer bus architectures that enables data to be sent directly from an attached device, such as a disk drive, to the main memory on the computer's motherboard. The microprocessor, or central processing unit (CPU) is freed from involvement with the data transfer, speeding up overall computer operation. DMA enables devices such as disk drives, external memory, graphics cards, network cards and sound cards to share and receive data from the main memory in a computer. It does this while still allowing the CPU to perform other tasks.Without a process such as DMA, the computer's CPU becomes preoccupied with data requests from an attached device and is unable to perform other operations during that time. With DMA, a CPU initiates a data transfer with an attached device and can still perform other operations while the data transfer is in progress. DMA enables a computer to transfer data to and from devices with less CPU overhead.An alternative to DMA is Ultra DMA, which provides a burst data transfer rate up to 33 megabytes per second (MBps). Hard drives that have Ultra DMA/33 also support programmed input/output (PIO) modes 1, 3 and 4, and multiword DMA mode 2 at 16.6 MBps.
