- Backing Storage
Backing storage devices
are where you can store data permenantly. This means that data is held when the
computer is switched off and can be loaded onto a computer system when required.
hardware that stores the data are called backing storage media. The media
are put into backing storage devices.
media in the table below are listed roughly according to their capacity. As technology
increases some of these capacities are constantly increasing and it can be difficult
to keep track of maximum storage capacities.
data stored on backing storage media can either accessed randomly (or directly)
or squentially. Random access means that the computer can go directly to a piece
of data. If the access is sequential then the computer has to go through every
item of data until it gets to the one it is looking for.
Disk Drive||Floppy Disk||1.44Mb||Random|
Flash Drive||Flash ROM||1
| || || || |
Disk Drive||Hard Disk||up
Disks are now rarely used, having been replaced by Flash ROM that can easily be
plugged into any computers USB port. The access time for Flash ROM is much faster
than that of a floppy disk, the capacity is much greater and Flash ROM is much
less likely to break.
CD's (Compact Discs) and DVD's
(Digital Versitile Discs) come in three different types. ROM's cannot never be
written to or erased. These are used to put on software or files that you never
want to change. A lot of software is bought on ROM discs. R stands for "recordable".
R discs can only ever be written to once, whereas RW (ReWritable) disks can be
written to and erased over and over again.
are built into computer systems. You can also buy external hard disk drives that
can be plugged into a computer system. External hard disks are replacing DAT tapes
as the most common method of backing up computer systems. This is due to their
direct access and larger capacity.