PS when I come to try it out, should I download the IomegaWare drivers for any of my Macs, or will it plug and play on OS 7.6, 9.1 and/or Tiger? (both the Scsi and USB one will work on the G3, so do both SCSI and USB need/not need drivers for 9 and X?) I was a little concerned that those drivers might add a ton of extensions to my slower Macs, so would prefer to avoid them unless absolutely necessary.
Okay, after some research, this is what works for me.
On 7.5.5, and 7.6.1, only a single extension, Iomega Driver version 4.2, 79K, needs to be installed. I believe that this extension will work for 6.0.8 and 7.1 according to my notes but cannot guarantee this.
On 8.6, it comes with Iomega Driver 6.0.2, should plug and play
On 9.2.2 it comes with Iomega Driver 6.0.8, should plug and play
On OS 10.3.9 the internal G4-400MHz Graphite Tower ATAPI Iomega Zip is plug and play, I have not yet tested my SCSI Zip on the SCSI out of the adapter card under either OS X or classic mode. I don't own a USB Zip.
And as you might expect, the SCSI devices all should be powered up before the Mac is powered up so they can get polled and initialized. Provided the driver is enabled and there are no SCSI ID conflicts, inserting media should cause an Icon to be mounted to your desktop with the usual properties of opening, dragging and dropping. Eject media by dragging to the trash. The front drive eject button is for ejecting media that is inserted without a powered up Mac. Amongst my modern Macs and PCs I have standardized on PC formatted ZIP media to keep things simple. The Iomega Tools that come with 8.6 and 9.2.2 in Apple Extras do some extra things that are strictly optional.
If you download the complete Iomega software package off the Internet particularly for the PC printer port parallel interfaced Zip drive you may get more than you bargained for. Days after I downloaded such a package on a Windows 98 machine I discovered a keylogger on my system!