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HARD DISKS
* Most PC's have an internal hard disk, but external disks may be
used too. External disks sit
alongside the computer in an extra 'box' with its own power
supplies and plug socket.
* An average PC may have 2Gb (230x 2 bytes = 1073741824 x 2 bytes,
i.e 2147483648 bytes). 1
Gb = 230 bytes. The standard size has increased dramatically over
recent years as ever more.
* IDE (Integrated Drive Electronics) and Extended IDE (EIDE) are
hard disk technologies
common on PC's
* More powerful and flexible are SCSI (Small Computer System
Interface, pronounced
'SCUZZY') and 'firewire' (1394). The difference between these
system lies in the way that data in
transmitted between the hard disk and the processor.
* A Zip Drive is a disk drive made by the Iomega Corporation. It
is a removable 100-megabyte
hard disk for PC's. the drive is suitable for backup, mass storage
or for moving files between
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computers. The company has recently started to manufacture a
larger Jaz drive, which takes 1
Gigabyte disks.
FLOPPY DISKS
* Modern PCs will also have one or two floppy disk drives. The
floppy disk provides a costeffective
means of on-line storage for small business computer systems.
* Floppy disk are used in the smallest microcomputer system as
well as with minicomputers and
are particularly useful in providing a means of decentralized
processing.
* A 'floppy' disk can be 3.5" in diameter or 5.25". A
3.5" disk can hold up to 1.44Mb of data.
TAPE STORAGE
. Like an audio or videocassette, data has to be recorded along the
length of a computer tape.
. In using tapes, it is not practical to read from and then write on
to a single piece of tape at the
same time.
. Reading and writing are separate operations, using separate heads,
and so two drives are
necessary for the two operations.
. Magnetic tape as a file storage medium is only practical when
every record on the file will be
processed in turn.
. Tape cartridges have a larger capacity than floppy disks and they
are still widely used as a
backing storage medium.
. They are generally measured in terms of tape width and length for
instance, an 8mm tape that
is 112m long can store up to 5Gb of data, a 4mm tape of 125m can
store up to 12Gb.
. Fast tape, which can be used to create a back-up file very quickly,
are known as TAPE
STREAMERS. Since tapes can only be updated by producing a
completely new carried
forward tape this provides an automatic means of data security.
CD -ROM (OPTICAL DISK).
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. It uses similar technology to the based laser based compact disc
audio system for data
storage.
. The capacity of optical disk is very compared with other media and
they are more difficult to
damage.
. The latest PCs are now automatically with a CD-ROM drive and some
software packages are
now only available on CD-ROM. CD-ROM stands for Compact Disc
Read-Only Memory.
This means that data is implanted onto the disc when it is made,
and subsequent users can
only retrieve information, they cannot alter or overwrite or
delete what is already on the disk.
. The speed of CD-ROM drive is relevant to how data can be
retrieved; an eight speed drive is
quicker than four speed drive. CD recorders are now available for
general business use with
blank CDs (CD-R). A CD-R can hold up to 650Mb. Once made, CD-ROMs
are not reusable
in the way that floppy disk are.
. However, a reusable disk (CD-RW) has recently become available.
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