With the lid off, we can see the Winchester Disc itself which occupies the top half of the casing.
The disc is a Seagate ST225, a 20MB Winchester Disc. It is known as a 5¼" half-height drive due to its physical size.
The interface used by this hard disc is ST506, a forerunner to SCSI.
In the 1980s, in contrast to nowadays, hard discs were very rarely physically perfect when they were sold and so on the front they had a Defect List which identified the bad sectors on the disc to be mapped out by the user at the formatting stage. This is a pretty good one with only one error.