applications software and
data is kept. Data stored on a hard disk can be
accessed much more quickly than data stored on a floppy disk.
A Hard disk spins around thousands of times per minute inside its metal casing, which is why it makes that whirring noise. Far less than a hairs breadth above the disk, a magnetic read and write head creates the 1 and 0s on to the circular tracks beneath.
Most hard drives are installed out of the way inside the computer, however you can also purchase external drives that plug into the machine.
Modern Hard drives are measured in gigabytes (GB). The most expensive computers will have the largest hard drives. Standard systems come with hard drives between 40Gb and 250Gb
It is also possible to add more than one hard disk inside a computer. In fact this is an excellent idea if you wish to back up your data whilst you work - the main disk holds your data whilst the second disk 'mirrors' it in the background. In that way when one of the disks fail (and they will !), the other is keeping your data safe.
There are two types of hard disks (standards):
IDE (Integrated Device Electronics)
 | Standard interface in PC's |
| More common than SCSI |
| Cheaper and slower than SCSI |
IDE is by far the most common standard, because it is 'good enough' for most purposes. However, if you wish for high speed and a more robust \ reliable system then SCSI offers an alternative.
SCSI (Small Computer Systems Interface)
| Faster - high speed of transfer than IDE |
| More reliable than IDE |
| Specialist card required |
| More expensive than IDE. |
Advantages and disadvantages of using hard disks as a storage media
Advantages
| Large storage capacity |
| Stores and retrieves data much faster than a floppy disk or CD-ROM |
| Data is not lost when you switch off the computer |
| Usually fixed inside the computer so cannot get mislaid. |
| Cheap on a cost per megabyte compared to other storage media. |
| Hard disks can be replaced and upgraded as necessary |
| Can have two hard disks in a machine, one can act as a mirror of the other and create a back up copy. |
Disadvantages
| Hard disks eventually fail which stops the computer from working. |
| Regular 'head' 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. |
This is a magnetic storage device
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