On 1/14/2016 5:44 AM, Micky wrote:
What wears out in an HDD? Is it only the tone arm that breaks? or
can the bearings the platter rides on break??? Good watches use
jewels, rubies, as bearings; and cheap watches use metal. What do
hard drives use?

I googled but couldn't find much about this. Does the spindle really
ride on an air cushion? Even when the drive is positioned sideways?


The heads ride on an air cushion, not the spindle. Any modern drive will
have an automatic unload system which causes the head actuator to retract
when the drive is powered down and the head arms are rested in a
'comb'-like rack right next to the edge of the platter. After the platter
spins up to speed the actuator moves the head arms off the rack and eases
them over the edge of the platters where the heads ride on a thin film of
air which spins along with the ultra-smooth platters thanks to miniscule
air foil shapes adjacent to the heads. There should never be any contact
and, thanks to the miniscule size of the heads in modern drives, any
contact will be disastrous.

In primitive drives the heads actually stayed over the platters and came
into contact when the drive spun down (anybody else remember the 'stiction'
problem in 10 and 20mb drives?) but the heads there were pretty beefy and
could stand a bit of rough treatment.