On Mon, Oct 24 2011, Michael Mol wrote: > On Oct 24, 2011 7:21 PM, "walt" <w41...@gmail.com> wrote: >> >> Now, lack of DMA is another story for hard disks, certainly. Here's >> where my ignorance of hardware limits my thinking: >> >> AFAIK the device driver *always* sits between the disk drive and the >> DMA hardware, doesn't it? > > DMA means a device is told where in the system's address space it may write > to, and it writes directly to that place without further CPU involvement. > Since drivers run on the CPU, the drivr isn't a go-between. > > When the CPU *is* involved in the passing of bits around, things slow down. > IIRC, that's called PIO--programmed IO.
Correct. DMA stands for direct memory access; the device has direct access to the memory. PIO is indeed the name when the CPU acts as a go between. allan
