Question about SCSI 2.5" HDs

[COCCORP at aol.com]

Hello listers...

Recently I was rummaging through some xtra SCSI powerbook HDs I have 
collected over the years. I tested them by hooking up a PB 100 to my PCI Mac via SCSI 
Disk mode.

So many seem to have problems being seen by the PB 100. Before I search out 
another PB to use as a tester (or before I go buy an adapter to use the 2.5" in 
a desktop mac), I wanted to ask the list might the PB100 be the problem?

Such as, is there a limitation to the kind of HDs the PB100 can see? Size? 
Maker of the 2.5" drive?

Thanks...

Craig W.