Ultra 320 SCSI

[Zac67]

SCSI usually is fully upward and downward compatble, there are very few devices that can't be adapted. There are adapters for wide (68-pin) or SCA-2 (80-pin) connectors which will allow them to connected to your SCSI controller.

Usually those drives work right away yet some of them require full bus width termination - with one of those you'd need an adaptor with integrated terminator (or half-terminator if it's in the middle of the bus). Newer drives (U2W onward) provide no device termination any more.

Alternatively, you can change your cable to a wide cable and use standard terminators on that with a single wide-to-narrow adaptor for the controller (that's what I did) - you could even continue using an SCA backplane.

Oh yes, and make sure you use SE or LVD/SE terminators; LVD only terminators won't work.

[Zac67]

There used to be a "differential" SCSI flavor with an extended reach and higher reliability in comparison to single ended (SE), the then standard. It was in limited use in datacenters and for special purposes.

When Ultra2 (U2W) emerged it introduced low voltage differential (LVD) to allow the higher frequencies required. The old differential mode was renamed to high voltage differential (HVD).

The point is, HVD isn't and can't be compatible with SE. Devices may very likely be damaged when connected to one another. There are converters/bridges to adapt the signals but they're extremely costly.

LVD devices on the other hand are predominantly compatible with SE (LVD/SE), with the SE mode limiting the bus to Ultra speed (20 MB/s for narrow, 40 MB/s for wide). Even if an LVD device at hand isn't compatible with SE nothing will smoke.