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Old January 14th 16, 07:38 PM posted to alt.comp.hardware,alt.windows7.general,comp.sys.ibm.pc.hardware.storage
Paul
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Default What wears out in an HDD?

JJ wrote:
On Thu, 14 Jan 2016 05:44:50 -0500, 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?


Most of the causes is due to combination of heat and force.

IMO, the arm and bearings and are pretty solid but it's not impossible for
them to break - depending on the material and manufacturing quality.

https://en.wikipedia.org/wiki/Bearing_(mechanical)#Service_life

Does the spindle really ride on an air cushion?


From where did you have that thought?


The spindle rides on a fluid cushion. Look for
information on FDB (fluid dynamic bearing) motors.

http://www.madshrimps.be/files/image...frey-21203.jpg

https://www.hgst.com/sites/default/f...aper_FINAL.pdf

FDB motors are available, where the shaft is fixed
on one end, or fixed on both ends. (Most of the
diagrams for these things are crap, and impossible
to figure out from the picture.)

FDB motors control NRRO (non-repeatable runout or "jiggling" :-) ).
Without the reduction in runout on modern FDB motors
(versus those using ball bearings), you could not have
your 4TB hard drive.

*******

The *head* floats on a cushion of air. And it's not really
a cushion shape either. There is a fairly small, fairly high
pressure zone near the head, that prevents contact (most
of the time).

The drive even has the ability to measure what that height
is, using "tricks" related to the signal sent to the head.
Some drives are able to detect a too-high flying height
on a write operation, and redo it. I don't have any data
on what percentage of drives have this capability. Drives
vary, in how many other drives they can tolerate
nearby, all jiggling at close to the same frequency.
Some "bargain" drives, might only be happy if they are
by themselves. Others are server rated, living in racks
with a lot of other drives.

*******

The mystery bearing in a hard drive, is the bearing
for the arm. Obviously, it needs to meet a decent
spec, due to flying height as the arm moves
from one part of the disk to another. And the
bearing could be quite conventional for all I know.
There's no "pumping action" to make an FDB there.

What you should be impressed with, is the cable that
makes the electrical connection from the arm, to the
PCB. That goes through millions and millions of
bending cycles. The engineering inside hard drives
is nothing short of amazing. Especially given the
low price of the bottom-end drives. Cheap and precise,
all in one modest package.

Paul