What are DMA modes?
DMA or Direct Memory Access means that the data is transferred directly between drive and memory without using the CPU as an intermediary, in contrast to PIO. In true multitasking operating systems like OS/2 or Linux, DMA leaves the CPU free to do something useful during disk transfers. In a DOS/Windows environment the CPU will have to wait for the transfer to finish anyway, so in these cases DMA isn’t terribly useful. There are two distinct types of direct memory access: third-party DMA and first-party or busmastering DMA. Third-party DMA relies on the DMA controller on the system’s mainboard to perform the complex task of arbitration, grabbing the system bus and transferring the data. In the case of first-party DMA, all this is done by logic on the interface card itself. Of course, this adds considerably to the complexity and the price of a busmastering interface.
DMA or Direct Memory Access means that the data is transferred directly between drive and memory without using the CPU as an intermediary, in contrast to PIO. In true multitasking operating systems like OS/2 or Linux, DMA leaves the CPU free to do something useful during disk transfers. In a DOS/Windows environment the CPU will have to wait for the transfer to finish anyway, so in these cases DMA isn’t terribly useful. There are two distinct types of direct memory access: DMA and busmastering DMA. Ordinary DMA relies on the DMA controller on the system’s mainboard to perform the complex task of arbitration, grabbing the system bus and transferring the data. In the case of busmastering DMA, all this is done by logic on the interface card itself. Of course, this adds considerably to the complexity and the price of a busmastering interface. Unfortunately, the DMA controller on ISA systems is ancient and slow, and out of the question for use with a modern harddisk. VLB cards cannot be used
