There are several reasons why platters are shrinking, and they are primarily related to performance . Reducing the hard disk platter's diameter by a factor of two approximately quadruples its rigidity. Imperfect platters lead to low manufacturing yield and the potential for data loss due to the heads contacting uneven spots on the surface of a platter. Smaller platters are easier to make than larger ones. For performance reasons, hard disk spindles are increasing in speed.
Smaller platters are easier to spin and require less-powerful motors.
They are also faster to spin up to speed from a stopped position. Smaller drives generally use less power than larger ones. IBM's amazing Microdrive has a single platter and is designed to fit into digital cameras, personal organizers, and other small equipment. The tiny size of the platters enables the Microdrive to run off battery power, spin down and back up again in less than a second, and withstand shock that would destroy a normal hard disk. Internal view and dimensions of the amazing IBM Microdrive.