Linux currently does not include full support for UDMA
(need to add CRC checking and error handling to do a proper job),
so it does not use DMA by default in your case.
You can still turn it on (hdparm -d1), and it will mostly work
but without full error detection/correction.
> OTOH linux and the bios both start my ST51270A on pio 4, which seems
> clearly correct as turning on DMA gives occasional timing errors.
Linux does NOT set PIO modes on drives (unless you use hdparm to do it),
so I am not sure what you meant by that.
-- mlord@pobox.com The Linux IDE guy