A dual floppy drive
device for Apple II
computers. This peripheral
was one of Apple's last 5.25" floppy drive
incarnations and was introduced in 1983
to sell with the Apple //e
The DuoDisk basically was a single unit that contained two 5.25" single sided double density floppy drives. It was exactly the width of an Apple //e, about 3 inches in height and around a foot deep (fit perfectly under a Monitor II). It sported the same beige color that the rest of the Apple family had at the time (save the Apple //c), and included a controller card for exclusive use with the drive.
The controller card that was included apparently was an early revision of the cards used for the single external 5.25 or 3.5" UniDisk drives. While the later UniDisk drives could be daisy chained to support more than one drive on a single interface card, the DuoDisk's included card could not, nor could the DuoDisk drive exist on one of these chains.
An interesting note is that apparently the DuoDisk drive was one of the most difficult peripherals from Apple to service. The construction and design was so tight, it required extra skill to open and service these drives without breaking anything. However, one advantage was that the individual drive speeds could be adjusted via screws accessible on the bottom of the drive without having to open the case. This was unlike the Disk II drive where one had to open the drive casing and find the right pot on the interface circuit.
While the DuoDisk was an improvement over the Disk II drive in size, it was was certainly louder in every operation, including realignment of the heads.