Rice Burner said:

So potentially the figure of performance for a disk drive is SPINDLE SPEED x SQUARE ROOT(AREAL DENSITY).

Now ... Correcting my Math in conclusion ... Doh:

In another words: A disk with twice the spindle speed should be equivalent in performance to the same disk with four times the areal density instead.

Thrax replied:

It is true, however as the spindle RPMs increase, the track density must decrease due to reliability concerns.

Now thats straight. Thanks.