It is all down to magnetism – the rest is mechanics and electronics! Your data at the most basic level is stored as a bit or binary digit. Each bit is either magnetised or not, respectively represented as a 1 or zero. Patterns of binary digits create data. For example the number 382 is a binary pattern 101111110 and the letter A is the binary number 1000001. Suppose your hard drive is 20Gb in capacity – then this has 160 thousand million bits.

These magnetic particles are stored on multiple laminated platters and are either magnetised or de-magnetised. Sometimes when erasing a hard drive it is referred to as ‘zeroising’. This is where all the magnetic particles are de-magnetised. In practise most applications that claim to do this actually do not. This is why we are able to recover data from hard drives that have been securely erased.

There are only a few basic parts inside your hard drive. The most critical is the read/write heads. An actuator arm swings these heads backwards and forwards across the platters as they are spun by a motor (typically at speeds up to 15,000RPM). The heads then read the magnetism of each bit in turn which represents your data. These heads rise fractionally above the disk surface as the motor gets up to speed and ride on a thin layer of air. When we refer to a head crash, this is where the heads have actually impacted the platters and caused damage to the laminated surface.

In order to interpret all these magnetic bits of data, a controller is required. This is essentially the ‘brain’ and it makes sense of the information fed to it by the read/write heads. An archiving system is also required so that the hard drive can easily retrieve data when required. In Windows, this archive is known as the File Allocation Table. All this logical information is controlled by the circuit board on the underside. In modern hard drives it is a myth that you can simply swap circuit boards when a hard drive fails given so much unique information in the ‘brain’. Indeed would you expect a human brain transplant to work?

With so much information stored in such a tiny amount of space on your hard drive and literally billions of variable patterns of binary data, this is why data recovery can be extremely complex. Similarly there is a lot to go wrong!