A hard drive is the most common mass storage device. It is used to save information for later use. At first, only the government and large corporations could afford them. Initially, they held 2 - 10 MB. Now, most hard drives hold 520 MB - 10 GB.

A hard drive uses electromagnets to store data. Negative and positive charges represent the 0s and 1s, of the binary code.

The platters are special metal disks that get the data magnetically stored on them. You can always read and write over data that is there. The read and write heads read from and write to the disk. The information will stay on the disk until it is written over. Remember never to put magnets near the computer.

When the computer starts up, it uses the BIOS to identify the hard drive. It then searches the boot block, the first section of the hard drive, which contains the initial start up files for the operating system.

The operating system then works with the controller to send and to receive data from the drive. It uses and individual address for each piece of data.

The hard drive is constantly moving. As soon as the computer is turned on, the platter begins turning at thousands of rotations per minute (rpm).

When the computer is turned off, it needs to be shut down correctly. This is done using the computer's shut down features, to store any data remaining in memory. Otherwise, the hard drive will stop immediatly, and will therefore be at risk for not functioning. Thie is because can cause the hard drive to deteriorate faster, or the heads to crash into the platters.