it's surely possible to use a UW scsi drive on a Scsi2 adapter. I'm using one seagate 68-pin UW and one IBM 80-pin U2W drive on my draco with a 80 to 68/50 adapter right now. The problem you would have is that this adapter is quite large to fit in a 1200 case. The 68 to 50 ones are alot smaller though and I think you could use one of those. There is no circuitry at all on those adapter, it's just pin-to-pin conversion as the protocol is still the same. Another problem I can think of is that scsi disks tend to run faster than IDE ones and thus produce more heat. I have no clue about the 2.5" ones though, as I have never seen one.
Justin
