Enabling DMA mode on IDE channels will consume less processor cycles almost reduce consumption of processor cycles from 50% to 5%. Windows 2K/2000 and Windows XP fail to enable DMA on IDE devices automatically. Though enabling DMA will not boost writing speed on to the disk, it will consume less processor cycles which can be used for another purpose.
By default PIO (Programmed Input-Output) transfer mode is set on IDE drivers in windows XP and 2000. PIO transfer mode consume more processor cycles because the central processor transfers data word by word or byte by byte.
When DMA transfer mode is enabled, small processor called DMA controller takes the burden of transferring data between IDE devices. Once the central processor starts the data transfer and transfers the control to DMA controller, the DMA controller looks after the data transfer and after completing the total transfer the control is transferred from DMA controller to central processor thus the central processor gets less involved in the transfer and so CPU cycles are saved which can be used by another programme.