What causes Bad Sectors on Hard Disk Drives (HDD)?

What causes Bad Sectors on Hard Disk Drives (HDD)?

There are 2 categories of reasons.

1. You (nothing personal)

If you jar or jolt or jerk or jiggle or strike or shake or bang your pc while it is accessing the disk, you can damage that tiny piece, and cause a bad sector. And your pc is pretty much always accessing the disk, so…

What’s happening is that inside the hard disk drive is a…disk, an actual platter that is spinning fast, really fast. The platter contains all the data. As the platter spins the “head” of the disk (that which reads and writes the disk) floats over the platter on a laminar cushion of air flow with literally a few nanometers of space between them.  That’s about 1 millionth of a millimeter. So, yeah, small.

For an analogy, it’s like a 747 flying 1/32nd of an inch off the ground.

Sudden motions of the disk (or the computer containing the disk) can cause the head to contact the platter and scratch it. Usually this only happens for a fraction of a second and damages just a tiny portion of the disk. Just a sector or few.

2. Entropy

The theory of entropy states that everything in the universe tends towards disorder (or decay).

This is happening right now on your hard drive as you read this 😉

The specific sources of this decay are:

  • original manufacturing defects
  • heat
  • wear over time
  • tiny, tiny specs of dust (that get by the filter)
  • vibrations of the building containing the device
  • electrical disturbances (from the power company, lightening)
  • error in the logic hardware of the drive
  • “overclocking”




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