Hewlett Packard C3013A Kittyhawk Disk Drive
Back in the good old days of the early 1990s, Hewlett Packard took it upon themselves to make a very small, cheap, low-capacity hard disk drive code-named Kittyhawk. It held 20 megabytes on two 1.3" platters, with a standard laptop-style IDE connnector.
The market was variously claimed to be PDAs, palmtop computers or gameboys. Unfortunately, none of these markets actually wanted the resulting product, so it died on the vine, so to speak. I picked up a few for pennies on ebay, and promptly dismantled one to allow the world to see what makes them tick.
Things to note:
The aluminum baseplate is not cast, it's milled. This is not at all common on disk drives, but this was a very small piece so it wouldn't cost much for this operation on a low-quantity product such as this.
Also, the little chip in the upper left corner of the PC board (the side with the white ring) is the fancy accelerometer controller that shuts down the drive when it gets bumped. The sensors are four little piezoelectric crystals (I guess) on the little brass arms next to the chip.