Hard disk drive (HDD)
A hard disk drive (HDD) is a storage device that records data magnetically on spinning platters and reads it with heads that fly just above the surface.
Inside the sealed case are one or more platters on a spindle, an actuator arm, and the read/write heads. A circuit board on the outside talks to the computer. While the drive is spinning, the heads do not sit on the platter. They fly on the air the platter drags round with it. When the drive stops, the heads move off the data surface.
How does a hard disk drive store files?
The computer sees a list of sectors. The file system decides which sectors belong to which file. The drive's job is to place the heads over the right track and read or write the magnetic signal. It does not know whether those sectors are a photo, a database, or an empty block.
Why do hard disk drives fail?
Bearings wear, heads degrade, the circuit board fails, or the platter surface develops bad sectors. A knock while the drive is running can cause a head crash. None of these is the same thing as deleting a file. Deletion is a logical failure, and the hardware can be working normally afterwards.
What should you do if a hard disk drive starts making a new noise?
Switch it off if it is clicking, grinding, or no longer appears in the computer. Do not open the lid, and do not keep restarting it to hear whether the noise changes. Note whether it was dropped, whether it clicked, and what the computer last showed.
Recovering files from a failed hard disk drive is a different subject from this definition. That service is described on the hard drive data recovery page.
What might you notice?
- A new click, grind, or beep
- The drive no longer appears in the computer
- Files that used to open now fail part way through
- The drive was moved or knocked while it was switched on