5. Hard Disk

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 it down properly.

Hard disks are measured in Gigabytes. A typical hard disk size will be around 120 Gb - 1 Terabyte.

It is possible to also have an external hard disk which can be plugged into the computer and used to back up your data and then stored in a different place to keep it safe.

Advantages

• necessary to support the way your computer works
• large storage capacity
• stores and retrieves data much faster than a floppy disk or CD/DVD
• Stored items are not lost when you switch off the computer
• Cheap on a cost per megabyte compared to other storage devices

Disadvantages

• Far slower to access data than ROM or RAM chips
• Hard disks can crash which stop the computer from working
• Regular crashes can damage the surface of the disk, leading to loss of data in that sector
• The disk is fixed inside the computer and cannot easily be transferred to another computer.