This next one is a bit of a bonus. It's a 2.5" 60 GB drive that I pulled out of a laptop when it flaked out. Fortunately the drive managed to recover itself long enough for me to retrieve the data. I was using it for a little bit as an emergency backup/transfer drive in an external enclosure until the motor made loud shrieking sounds and finally seized up on me.
As you can see from this shot, 2.5" form factor drives are pretty small. This one has 3 times the capacity of the 3.5" form factor drive from Part 2.
Under the cover it's like a miniature version of the larger drives. Like the Deskstar, this one also uses an off-platter landing zone. This drive has two platters.
Unlike the larger drives, this one only has one magnet, presumably for space reasons. It's just as strong as the magnets in the larger drives though.
The fully disassembled drive and its two platters
A close up of the read/write heads, one pair for each platter.
Size comparison of two drive arms