Question

I was using my computer the other day and it suddenly started to make a high-pitched squealing sound and then stopped working. When I took it in for repair, the service guy said that my hard disk had had a "head crash" and died, taking all of my data with it. What happened?

Answer

In the HSW article entitled How Hard Disks Work, you can see that the read/write heads are touching the platters in the drive. When the platters spin up, they rotate at anywhere between 3,600 RPMs and 7,200 RPMs. To the head, the platter seems to be moving at about 150 MPH and a very thin cushion of air forms between the head and the platter so that the head "flies" over the platter. If even the smallest bit of dust makes its way onto the platter, the flight is disrupted and the head "crashes" into the platter, scratching it. Of course the crash sprays a lot more dust and debris onto the platter and then it's all over.

The other thing that can cause a squealing sound is the bearings in the drive motor. That is another common way for a drive to fail.

Hard disks are amazingly reliable these days, with "Mean Time Between Failures" (MTBF) of 500,000 to 1,000,000 hours. That means that, on average, a drive fails after the specified number of hours, with half the drives lasting more than that and half lasting less. 500,000 hours is about 57 years. It is a fact that a drive may last much less than 57 years, however, so frequent backups are important.

See How Hard Disks Work for more information on these amazing devices!

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