Why does mechanical failure causes HDD being undetectable by bios or OS?

[andy]

Hello!

Could someone please explain why in the case of *mechanical* failure HD
becomes sometimes undetected by BIOS and/or the operating system (e.g. win xp
or linux)?

If it was an electronic failure then such behaviour would be obious, but why
the same happens with some mechanical failures? When electronics is working in
my opinion it still should be detected by bios and/or the system (win xp or
linux), but often it is not.

I could recover about 80% of the data from my HDD (which apparently has a
mechanical failure - plates spin up and down, heads create bad noises) if only
the disk could be seen by the system all the time. But often during copying of
the data heads hit with a loud sound so badly that sometimes even the plates
stop rotating, and the disk then dissapears from the system. It is then very
difficult to make it detectable by the system again, sometimes the sytem can
detect it but only after several minutes of copying it freezes and then
dissapears again.

Recently, I was unlucky, and even after several dozens of retries it's still
undetectable by the system.

Could you please advice what to do to make the disk detectable by the system
all the time?
What causes that it is not detectable although the failure is in mechanics not
electronics?

BTW, if someone has the same disk model (Quantum Fireball ST64A011), please
let me know.

andy

[Kenabi Tsuki]

not sure how useful it'll be in the long run, but try putting it in the
freezer for half an hour before you attempt to try again (makes all the
components shrink some. including bearings, platters[depending on
substance they're made of], head arms, etc.) and in cases where it's not
the circuit board having issues, it can give you a slightly better
chance of getting the full 100%.

i should know, i went through this less than a week ago ;)

-Tsuki