This article is from the Apple II Csa2 FAQ, by Jeff Hurlburt with numerous contributions by others.
For the UniDisk 3.5 (model number A2M2053), you need either Apple's "SuperDrive" card or the "Liron" card. The UniDisk 3.5 is quite rare. It is a clean white color instead of greyish "platinum". It also has the eject button just above the line of the disk insertion slot, with a separate manual ejection hole. The "Liron" card's official name is "Apple 3.5 Floppy Disk Drive Interface Card". It has the word "Liron" on the back (which is the nickname of the IWM disk controller chip, if I remember right). For the Apple 3.5 Drive (model A9M0106 as used on the IIgs), you need either Apple's "SuperDrive" card or the third party "Universal Disk Controller" card. The drive is platinum in color and has the eject button in line with the disk insertion slot and the ejection hole is in the middle of the button. The "SuperDrive" card's official name is "Apple II 3.5 Disk Controller Card". The card has an LED on top, and has its own processor, RAM and ROM. For the Apple SuperDrive, you need the "SuperDrive" card. Model ID is inconsistent. Check for something like "Family number G7287". The SuperDrive looks exactly the same as the Apple 3.5 Drive. It supports 1.44 MB high density and 720 KB double density disks as well as the 400 KB and 800 KB formats. You can use a SuperDrive with the Universal Disk Controller card, but you won't be able to use its extra capabilities, and it will behave like an Apple 3.5 Drive. By: O Aaland and Michael Pender