David Empson wrote:
There was also at least one third party card, the Universal Disk Controller. It supports the Apple 3.5 Drive and 5.25" drives. Early models support the UniDisk 3.5, but I'm not sure about support for Macintosh drives.
To be precise: It's not a hardware difference that difference that determines whether or not the UDC supports a UniDisk 3.5. By using the EPROM image from an older card, you can run the UniDisk on a later "short" UDC card (has custom ASIC to replace a lot of TTL logic).