What is a hard drive

What is a hard drive? - Structure simply explained

Everyone has it in their PC: the hard drive. But what exactly is a hard drive? We explain the structure and functionality of the data carrier using examples in a simple and understandable way in our guide.

A hard drive is a fascinating piece of technology and the most popular data carrier when it comes to storing large amounts of data. But what is a hard drive anyway?

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What is a hard drive?

A hard drive,Hard disk (HD)orHard disk drive (HDD) is a small rectangular drive that can be attached to the computer. Their main job is to store data and files. The company IBM had developed the first hard drive in 1956, which had 3.75 MB of storage capacity and the dimensions of a wardrobe (173 x 152 x 74 cm). Today, hard drives are available as a handy 3.5- or 2.5-inch drive, with 2 TB storage capacity and above being the standard.

But how does a hard drive work? To understand this, one has to look at their structure.

Structure of a hard disk

Danger: Never unscrew a hard drive. Inside there is purified air that is practically free of fine particles. If it escapes, the plate will stop working. See also hard drive broken: Can the data still be saved?

If you unscrew a (defective) hard drive, you will see one or more "platters", similar to an old record player. There is a mechanical arm (actuator) on which read and write heads are attached. The actuator positions the heads so they can write and read files. The hard disk rotates at speeds of around 5400 to 7200 revolutions per minute (90 to 120 revolutions per second). Due to the speed of rotation, the actuator hovers a few micrometers above the platter surface so that it does not scratch it.

Example 1: You are copying a very large file of 1 TB onto your hard drive. If the hard disk is still new, the write head starts at the beginning and writes the entire file to the disk one after the other. Because a hard drive always writes sequentially, if possible, i.e. the data nicely one after the other - in contrast to the SSD.

Example 2: If the hard disk is in use, data has already been added and deleted. This created “gaps” in the tracks on the hard disk. If you now copy a very large file to the disk, it begins to write the file again, but only in the remaining gaps.

So that the hard disk later knows where all the “pieces” of a file are, it needs a controller and a small internal memory. The electrical engineering required to control the hard disk and its mechanics is on the back: Here you will find a small circuit board, similar to a motherboard, where the cache and flash memory as well as the motor and SATA controller are installed.

Info: The more “fragmented” the data is on the hard drive, the slower it reads and writes data. To rearrange the files coherently, you can defragment the hard drive.

How is data stored?

There is a layer of iron oxide on the surface of the plate. This is magnetized and changed by small magnets on the read and write head of the hard disk. In this way information can be stored and read.

Note: And that's exactly why strong magnets should be kept away from hard drives, otherwise the data can be irretrievably lost.

You don't notice much of this in Windows itself. You can only hear the hard drive starting up and shutting down when you turn on the PC, with a low whirring or beeping sound.

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