Well I've just tried an ATA100 on an ata33 board and it hung in the
BIOS. No
ways could I get it to boot.
Very odd .... I'm using a toshiba UDMA100 on DMA(33) machine just fine.
Have a look at the manufacturers' websites for info on the drives and possible utilities to set the bus speed.
I had some fun with a couple of different UDMA100 drives last year. The first one I bought would not work on DMA33 (even with the 80 pin cable - that is another thing to get right but you probably know that although I mention it just in case). Exchanged it for a different make which worked fine.
Digging around on manufacturers' web sites revealed the reason for this odd behaviour. The drive may be set to UDMA100 by default - in which case it is unlikely to work out of the box on DMA33. A DOS utility is used to configure it. Alternatively, a drive may be set to DMA33 at source and possibly not be running at optimum speed when used on a UDMA100 bus unless configured.
HTH Syd