Yup...narrow diff is well defined. There's an X-Y matrix of SCSI standards that have X == single ended or differential and Y == [ async narrow (5Mb/s), sync narrow (10Mb/s), sync wide (20Mb/s) ]. Once you get to wide fast, Ultra SCSI (aka SCSI3) and LVD SCSI, et. al., things get a bit odd. My Sun SS20 has a nice wide diff SCSI controller (20Mb/s) with a 4GB Seagate disk. Makes a big difference over the narrow internal drives. Ken Seefried, CISSP