Introduction — continued
Here I've removed the screws holding the top cover and rotated the cover up and off. The black box with a white center that's mounted to the cover is an air filter for the breather hole. The breather ensures that there is no pressure differential between the inside and outside of the drive. However, a simple hole would allow dust, smoke, and other such contaminants to get inside the drive, causing Very Bad Things to happen. Thus, we have a filter.
It's difficult to see the platter itself in this shot, but you can at least see the ring directly under the drive head. You might think that this ring indicates the head has contacted the surface of the platter (i.e. a head crash) but actually, this is an area of the platter reserved for "parking" the head when the drive is powered down.
Normally, the head swings back and forth across the surface of the platter to read data from it, but as soon as power is removed, the head automatically pivots over the reserved area of the platter. That way, if the drive experiences a physical shock while the computer is off, the head doesn't come in contact with a part of the platter that holds actual data.
Here's a final close-up of the drive that gives you a slightly better view of the platter. Believe it or not, the surface of the platter is mirror-like, though it doesn't show very well in these photos. In higher capacity drives, there might be additional platters stacked on the spindle, but this is only a 40GB drive, so it makes do with a single platter. You can also see flecks of dust on the platter itself. It would be a disturbing sight if the thing weren't already garbage.
So there's a quick breakdown (literally) of a modern hard drive. Don't try this at home, kids. Well, unless it's an IBM 75GXP or 60GXP, in which case you can tell yourself that it was only a matter of time anyway.