What is DMA / UDMA?
Direct Memory Access / Ultra Direct Memory Access refers to a technology that allows a hard disk to manage data transfer without the aid of the CPU. This speeds up data transfers, while also leaving the CPU to perform other tasks. DMA / UDMA have gone through many iterations, the latest being UDMA 6, which offers transfer speeds of 133 Megabytes per second. DMA / UDMA modes are specified in the ATA standard. To achieve speeds above 33 Megabytes per second, as envisaged in UDMA3, a special 80-pin conductor cable is needed to reduce the interference that occurs between two data-carrying channels. Though the data is transferred using only 40 pins, the remaining pins are needed to ground interference created during the data transfer.