How Does a Hard Disk Sector Become Damaged?
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Hard Drive Structure
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A hard drive is a collection of disks known as platters and one or more moving read/write head that stores and retrieves data. The platters have concentric rings called tracks that each have a small bit of information on them. Each track is further subdivided into sectors. The platters themselves have a thin protective coating that is meant to protect the data from accidentally being scratched by the read/write head or dust or other contaminants.
Head Crashes
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The most infamous and catastrophic sort of hard-drive failure is a head crash. The read/write head sits only millimeters above the surface of the platter, which can be spinning at more than 15,000 revolutions per minute in some drives. If a piece of dust gets in past the air filter and clings to the drive, it can jar the head as it passes by, sending it careening back down into the platter. Similarly, if the computer is dropped, the head can collide with the disk. This can damage the sectors and the write head, sometimes completely destroying a hard drive.
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Wear and Tear
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Sectors go bad from more ordinary causes more often than you might be aware of. Heat, oxidation, damage from dust and other factors take their toll. A sector does not have to be completely unreadable to be "bad." Sometimes, it is simply slow and difficult to read, making the data on it less secure and accessible and slowing down the hard drive. Hard drives typically come with a number of extra tracks. When a sector goes bad, the drive stores its data on one of the extra tracks, and the user never knows. When you start to get bad sector warnings in your computer, however, it means things are getting serious. The hard drive has used up all of its spare sectors already, and more are going bad. You should back up your data and get a new hard drive.
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