k wrote:
] [ What i didn't know is that the platters were plastic (glass?).
] In all the harddrives i've ever opened, they were metal,
] presumably aluminum. -k]

The migration to glass platters began in the last decade. Further explanation is at

http://www.storagereview.com/guide2000/ref/hdd/op/mediaMaterials.html

Briefly:

As technology advances, the gap between the heads and the platter is decreasing, and the speed that the platters spin at is increasing, creating more demands on the platter material itself. Uneven platter surfaces on hard disks running at faster speeds with heads closer to the surface are more apt to lead to head crashes. For this reason many drive makers began several years ago to look at alternatives to aluminum, such as glass, glass composites, and magnesium alloys.

It now is looking increasingly likely that glass and composites made with glass will be the next standard for the platter substrate. IBM has been shipping drives with glass platters for several years ...

Hard Disk Drive Platters are Glass