Apple II FAQ

Adrian wrote: I think that works. The older Mac 800K external drives, in the very slim beige case, don't have a pass-through connector, so they have to be last in the chain, which means IIRC that you can't combine them with 5.25-inch drives, since the 5.25 inch drives must follow any 3.5-inch drives. The newer Apple 3.5 Drive has a pass-through connector. The Apple FDHD or Superdrive will work just like an Apple 3.5 drive, but the IIgs disk controller doesn't support the 1440K mode. Apple sold a separate "Apple Universal Disk Controller" (or some such thing) that could support 1440K mode. The Apple UniDisk 3.5 should also work, but it is less optimal. It has a built-in smart controller, but because it's too smart (or not smart enough), the software has to poll it about once a second, and it makes noise every time this happens. Note that the Apple II models other than the IIgs cannot support any 3.5-inch disks other then the UniDisk 3.5 unless you use a suitable controller card. The Disk II controller card only supports 5.25-inch disks.