Thanks for the detailed reply, it helps. I read up on SCSI termination methods, and it makes some more sense now. Maybe all the people who've used an external Zip 100 with a Plus also had some additional SCSI device with active termination, but just never mentioned it?

I'll take another look at the SE/30 internal drive termination and jumper settings.

One thing I'm a bit confused about: in a single-drive system like the SE/30 with an internal HD, the HD will be terminated and the SCSI controller on the motherboard will be terminated, right? Those are the two sends of the chain. If I then connect an external SCSI device and terminate that, it stands to reason that I'd need to disable termination somewhere else. Would the internal HD mark the other end of that chain, or the motherboard controller? Is there some kind of auto-termination on the motherboard controller maybe? If not, then anyone adding an external SCSI device to a Mac that already contained an internal SCSI HD would have had to crack open their Mac and change some termination settings, which I don't ever remember doing back in the day when these machines were current. In fact I know I added an external SCSI CD-ROM to a Mac SE that had an internal SCSI HD, and I never once opened up that Mac.

I'm beginning to understand why SCSI died off.