> 
> wd0 at pciide0 channel 0 drive 0: <Maxtor 51536H2>
> wd0: drive supports 16-sector PIO transfers, LBA addressing
> wd0: 14655 MB, 16383 cyl, 16 head, 63 sec, 512 bytes/sect x 30015216 sectors
> wd0: 32-bit data port
> wd0: drive supports PIO mode 4, DMA mode 2, Ultra-DMA mode 5 (Ultra/100)
> wd1 at pciide0 channel 0 drive 1: <WDC WD102BA>
> wd1: drive supports 16-sector PIO transfers, LBA addressing
> wd1: 9779 MB, 16383 cyl, 16 head, 63 sec, 512 bytes/sect x 20028960 sectors
> wd1: 32-bit data port
> wd1: drive supports PIO mode 4, DMA mode 2, Ultra-DMA mode 4 (Ultra/66)
> wd0(pciide0:0:0): using PIO mode 4, Ultra-DMA mode 5 (Ultra/100) (using DMA
> data transfers)
> wd1(pciide0:0:1): using PIO mode 4, Ultra-DMA mode 4 (Ultra/66) (using DMA
> data transfers)
> 
> starjumper 501# dd if=/dev/rwd0d bs=64k count=16384 of=/dev/null
> 16384+0 records in
> 16384+0 records out
> 1073741824 bytes transferred in 32 secs (33554432 bytes/sec)
> starjumper 502# dd if=/dev/rwd1d bs=64k count=16384 of=/dev/null
> 16384+0 records in
> 16384+0 records out
> 1073741824 bytes transferred in 47 secs (22845570 bytes/sec)
drives are different.

but in fact it DOES depend of udma mode with drives slower that 33MB/s

for example my drive (seagate 20GB) on my VIA MVP3 motherboard with
UDMA/33 has 13MB/s transfer speed, with same CPU with intel based
motherboard gets 21MB/s (UDMA/33 too), on HPT336 gets 29MB/s