Vintage Apple Unidisk, External,5.25" Floppy Disk DriveModel No. A9M0104, Serial No. K1G9927Tested: It powers up.
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Here is some of the history of this disk drive taken off the web from Wikipedia:

TheDisk II Floppy Disk Subsystem, often rendered asDisk ][, is a 5¼-inchfloppy disk drivedesigned bySteve Wozniakand manufactured byApple Computer. It went on sale in June 1978 at a retail price of US$495 for pre-order; it was later sold for $595 including thecontroller card(which can control up to two drives) and cable. The Disk II was designed specifically for use with theApple IIpersonal computerfamily to replace the slowercassette tapestorage and cannot be used with anyMacintosh computerwithout anApple IIe Cardas doing so will damage the drive or the controller.

Apple produced at least six variants of the basic 5¼-inch Disk II concept over the course of the Apple II series' lifetime: The Disk II, the Disk III, the DuoDisk, the Disk IIc, the UniDisk 5.25" and the Apple 5.25 Drive. While all of these drives look different and they use four different connector types, they're all electronically extremely similar, can all use the same low-level disk format, and are all interchangeable with the use of simple adapters, consisting of no more than two plugs and some wires between them. Most DuoDisk drives, the Disk IIc, the UniDisk 5.25" and the AppleDisk 5.25" even use the same 19-pin D-Sub connector, so they are directly interchangeable. The only 5.25" drive Apple sold aside from the Disk II family was a 360k MFM unit made to allow Mac IIs and SEs to read PC floppy disks.