The hard disk is the main storage device in your computer. It is a bit like a filing cabinet: all of your data files and applications software are stored on it.
The hard disk contains a number of metal platters which have been coated with a special magnetic material. The data is stored in this magnetic material. Thus, the hard disk is known as a magnetic storage device.
In order to access the data, the platters spin many thousands of times a second and a magnetic read and write head floats just above the surface of the platter.
When you hear the term 'hard disk crash', this refers to the read/write head crashing down onto the surface of the hard disk. There is a risk every time this happens that the data stored in the section just where the head crashes might be damaged. That is why it is a bad idea just to switch the computer off at the wall without shutting…