Head crash
A head crash is physical contact between a hard disk drive's read/write heads and the magnetic platter surface.
In normal use the heads of a hard disk drive fly just above the platter on a film of air. A head crash is that flying height collapsing, so the heads touch the surface. The contact scrapes the magnetic coating that holds the files, and it often damages the heads as well.
How does a head crash happen?
A knock while the drive is spinning, a failing head, or dirt inside the drive can bring the heads down onto the platter. Once contact starts, the platters keep turning underneath, so a scratch can spread within seconds.
Why does a head crash lose files?
The files live in the magnetic coating. Where that coating has been scraped away, those sectors no longer hold a readable signal. Debris from the contact can then be dragged across other parts of the platter.
What should you do if you suspect a head crash?
Switch the drive off and leave it off. Do not keep powering it on to see if it comes back, and do not run a software scan against it. Each spin can grind the damaged area further.
A repeating click is one sign people notice first. The clicking hard drive page describes that symptom.
What might you notice?
- A repeating click, scrape, or buzz
- The drive spins and then falls silent
- The computer no longer sees the disk
- The drive was dropped or knocked while it was on
Related terms
Common misconceptions
Is every click a head crash?
Occasional soft clicks can be normal drive activity. Persistent hard clicking, grinding, or scratching is a reason to stop using the drive. The sound alone does not establish that a head crash has occurred.