A2 3.5 Drives
3.5" Floppy Drives
Apple made two different 3.5" drives for the Apple II, the AppleDisk 3.5" and the UniDisk 3.5". The AppleDisk 3.5" is Apple Platinum colored and was introduced along with the Apple IIgs. With exception of the //c and the Liron card, it is compatible where a 3.5" drive is supported on the Apple II.
AppleDisk 3.5 (A9M0106)
This is an external Apple 800K DSDD 3.5" GCR . It can also read 400K disks. Drive. See the compatibility chart after the UniDisk 3.5" information for more detail.
Apple UniDisk 3.5 (A2M2053)
This is an External Apple 800K DSDD 3.5". Compatibility with the following computers is as follows:
The UniDisk 3.5" can be used on the following Apple II Systems, and it's requirements are listed with it.
The UniDisk 3.5" drive is NOT COMPATIBLE with the Laser Universal Disk Controller. It will do Bad Things when it's plugged in. Do Not Try It.
Another way is to turn on the computer, when you can see the monitor hold down both the Open and Closed Apple keys. (Opposite sides of the spacebar) and hit CTRL and RESET. If the computer goes into a checkerboard type pattern you have the new ROM installed. If the computer goes to an alternating vertical line pattern with a click between each alternation. (Turn up volume, on left side, under keyboard). You will need a ROM upgrade. The part # for this ROM upgrade is 342-0033.
Apple IIc Plus.
The UniDisk is not the recommended 3.5" drive for use with an Apple IIgs although it will work fine for normal usage. It will be slower than using the recommended drive, the AppleDisk 3.5". It looks similar to the UniDisk 3.5" and is the same color as the Apple IIgs itself. Using a UniDisk on a IIgs while using any GS specific software that runs under GS/OS will require that a device driver be installed on the boot volume as well. The driver, titled 'UniDisk.3.5' can be found on the system disk set and be installed using the installer on the System Tools disk of System Disk 5.0.4 or the Installer disk of System 6.0. Using the UniDisk on the IIgs will also be slower than using the proper 3.5" drive and some disk based software from such groups as the FTA may simply not run.
Apple DuoDisk 3.5 (Unreleased)
This is an External Dual Stacked Apple 800K DSDD 3.5". It is the same design as the UniDisk 3.5" except that it is 2/3rds taller and contains a second drive assembly. Both the UniDisk and DuoDisk 3.5" use the same internal controller card. One could make a DuoDisk 3.5" by simply adding the missing components to the internal controller card as well as a second "Black Label" 800K drive assembly. Of course you would need to do something about the case, too. Perhaps some good plastic work can be done to make your own case.
Apple FDHD / SuperDrive 3.5 (G7287)
The FDHD ('FudHead') / SuperDrive was introduced for the Macintosh and is not an Apple II specific 3.5" drive but due to it's nature it is compatible where an AppleDisk 3.5" (A9M0106) would otherwise be appropriate and requires a separate controller card, the Apple II 3.5" Controller Card, Apple P/N A0076LL/A in order to function as a High Density drive on an Apple II. There is no solution for high density drives in any Apple II that does not have expansion slots with exception of the Mark Twain, prototype IIgs which has an on board SuperDrive controller.
Haba Systems HabaDisk
The HabaDisk is a 3.5" 320K drive that uses the Apple Disk ][ or compatible controller.
Amdek AmDisk I, III
Amdek, known more for monitors, also brought a 3" (3 inch) drive to market for the Apple II and Atari, for the Apple II it used a standard Disk ][ controller. The AmDisk I was replacement for the Disk ][. Down to the fact that if you want to use the back side of the disk you had to remove it and turn it over.
The AmDisk III was a 360K double sided drive system that was marketed for the Atari and IBM PC, it was supposed to come to the Apple II but never did.