For mobile applications, the emphasis is on power and
environmental robustness, with slimness and low weight being
desirable. The favorite design is a ‘2.5-in. form factor’ with one or
two 65 mm diameter disks spinning at typically 5400 rpm. For
desktop applications, price per gigabyte rules and the favorite
design is the ‘3.5-in. form factor’ with up to five 95 mm disks
spinning at 7200 rpm. For ‘server’ or enterprise applications, the
emphasis is on performance (data-rate and accesses per second)
and on reliability, with power becoming an increasingly important
consideration. Here there is more variety of both form factor and
disk diameter. Spindle speeds are much higher at 10,000 or
15,000 rpm and the actuator access times are correspondingly
shorter.