Quoting from the Linux Zip Drive mini-HOWTO:So if you rip one apart, there's a standard 50-pin internal SCSI drive inside?
8.8 Can I use the parallel drive as a real SCSI disk ?
The PPA-3 parallel-to-SCSI adapter is implemented as a single ASIC chip that Iomega calls a VPI0. It is embedded on the ZIP drive's controller card. There is an actual SCSI bus present, but not in a useful form.
Although I haven't tried to compare the two cards, it seems logical that the VPI0 replaces the conventional electrical buffering circuits that would be required if the SCSI bus were extended outside the package.