One is the usual crash most often sited on external drives. While some may be simple "replace the case" failures, ALL of these will be labeled as "My HDD crashed."
The other type of crash is file or file system corruption. Again I would write that's not a HDD crash, it won't matter to the average owner.
My thought here is about 1/2 of all crashes are not true HDD crashes. Then again you find folk continue to have no backup plan.
Bob
I have owned PCs since my first Packard Bell in 1991 and never had a hard drive crash until 2010. Up until now, my hardware has outlasted the OS. Today, reading the forums, I get the impression that the current generation of PC users accept HDD crashes as a normal occurrence. My Dell XPS8000 is on its third HDD which also just failed. I would like to know WHY these hard drives are failing. So far in the forums all I can find is how to recover from a crash, not how to avoid them. Please enlighten me. Thank you.

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