Every hard disk contains one or more flat disks that are used to actually hold the data
in the drive. These disks are called platters (sometimes also "disks"
or "discs"). They are composed of two main substances: a substrate
material that forms the bulk of the platter and gives it structure and rigidity, and a magnetic
media coating which actually holds the magnetic impulses that represent the data. Hard
disks get their name from the rigidity of the platters used, as compared to floppy disks
and other media which use flexible "platters" (actually, they aren't usually
even called platters when the material is flexible.)
The platters are "where the action is"--this is where the data itself is
recorded. For this reason the quality of the platters and particularly, their media
coating, is critical. The surfaces of each platter are precision machined and treated to
remove any imperfections, and the hard disk itself is assembled in a clean room
to reduce the chances of any dirt or contamination getting onto the platters.
Next: Platter Size
