What happens when a hard drive crashes

0309 primary hdd crash

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When Manoj Yadav took his dead PC to a repair shop, he was told that the drive had crashed. He asked me what physically happens to a drive to crash it.

Hard drives, unlike the SSDs slowly replacing them, are mechanical machines with moving parts. Each drive has one or more spinning platters, extremely tiny magnetic read/write heads, two motors, and a fair amount of circuitry. When working properly, one motor spins the platters at a very fast speed—usually 5400rpm or 7200rpm. The other motor moves the read/write head in and out with microscopic precision. The head doesn’t come into physical contact with the platter, but it floats on a cushion of air that may be as little as five nanometers. That’s less than 0.0000002 inch.

It’s a wonder they work at all.

[Have a tech question? Ask PCWorld Contributing Editor Lincoln Spector. Send your query to answer@pcworld.com.]

Today, we describe a drive as having crashed if it suddenly stops working—no matter what caused its death. But the word originally comes from one particular problem: A head crash.

That’s when the drive’s read/write head comes into physical contact with the platter—the microscopic equivalent of an airplane hitting the ground so hard that it scrapes the asphalt off the runway. In a head crash, the head scrapes off the magnetic coding containing your data. Whatever files were on that part of the platter are history.

0309 hard disk head crash Alchemist-hp

Hard disk head crash

But there are other, less spectacular mechanical crashes. If the head alignment goes off by just a few nanometers, the drive could become unusable. In this case, however, it’s possible for a skilled technician with the right equipment to recover your files.

Either type of crash can be caused by a sudden impact, such as dropping the drive. If the drive is powered up and running, even a slight move can cause damage. But even if your drive never suffers anything cataclysmic, general wear and tear can eventually crash it.

Not all crashes are mechanical. The circuitry can also wear out over time, especially if your PC frequently overheats.

Here are a few tips to help you avoid or survive crashes:

  1. Handle a hard drive, or a laptop containing one, carefully.
  2. Avoid moving a PC containing a hard drive unless the PC is off or in sleep mode.
  3. Protect your PC from overheating.
  4. Back up daily.
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