

IDE does not do DMA.  This is because it's like te PC AT hard disk
interface.  The controller moves a sector to some buffer memory on the
controller card, then the CPU moves the data from the buffer to main
memory where it's needed.  If IDE doesn't work this way, then it's not
compatible.

Heck, if IDE used DMA, then you'd hear all kinds of complaints about
ISA bus systems with more than 16M RAM not working with their IDE
drives.  16M is the DMA addressing limit of the ISA bus, and if IDE
did DMA there would be trouble.

(BTW, there are DMA-enabling signals in the IDE cable spec, but the
last report I heard was that they are never implemented, because it
would require a different kind of IDE adapter and different drivers.)