If you finish some work on a computer you often want to save
it so that you can look at it again sometime. But how does the computer store
data? You may want to transfer your data from one computer to another - so
you save the data to a disk and load it into another computer. How does this
work? You want to put a new piece of software onto your computer - how will
you copy the software on and where will it be saved when you switch the computer
All these questions are related to the ways in which computers
One of the first methods of storing data and software
for use on a computer was the use of punched paper tape. The tape
was fed through a special tape reader and the rows of dots converted
Punched cards were also used to store data. These were
sometimes punched by hand and had to be entered into the computer
in the correct order ... if you dropped the cards and they became
disordered then you may have had to start all over again.
Each dot corresponds to a BInary digiT (or BIT) of data.
Eight bits in a group are called a BYTE (some people refer to half
a byte, or 4 bits, as a NYBBLE).
The problem with paper tape was that it kept on breaking
- since the more holes that you punched in it the more fragile it
Another problem with paper tape was that the large size of the holes
on the paper meant that you needed very long lengths of tape to store
lots of data or small computer programs.
Magnetic tape works along the same principles as paper
tape. However, the tape is made of a thin film of plastic with a magnetic
covering on it. Instead of holes punched into the tape there were
much smaller areas of magnetised and non-magnetised tape.
This proved to be so successful that magnetic tape is
still used today - not as much in computing but the videotapes that
you use to record films on are made of the same material.
Magnetic tape had a problem though. Just like when you want to fast
forward to the end of the film you have to wait for the tape player
to wind on all the film ... the same thing happened if you wanted
some data at the end of the tape: you had to winf all the way through
the whole tape.
This was very time-consuming.
Magnetic (floppy) Disks
To solve the problem of magnetic tape - the two ends
of the tape were joined together to form a magnetic disk.
If you take an old, broken floppy disk apart you will find inside
of it a circular sheet of plastic. This is the same material that
made up the magnetic tape. Now, of course, a circle doesn't have any
ends so it is much quicker to find your data - wherever it happens
to be on the disk.
The first magnetic disks were stored in a card sleeve
(there's one shown here in the photo) and it allowed the disk to bend
slightly ... this is why they were called 'floppy' disks. The problem
was that this flexibility often meant that the disks became bent and
Floppy disks were useful but they couldn't store a lot
of information. Hard disks (originally called Winchester Disks) also
stored data on a set of disks by a number of magnetic sections - in
just the same way as floppy disks did.
However, the hard disk is made out of metal and it is coated in a
magnetic material. The whole disk is enclosed in an airtight, dustproof
container. This allows the disk to spin round at a much greater rate
than the floppy disk does. The disks in a hard disk unit also spin
the whole time the computer is switched on (this is most likely what
you hear when the computer is on).
The advantage of magnetic media (tapes, floppy disks,
and hard disks) is that data can be saved easily. It can be deleted,
and new data stored on top of it.
It is possible to store much more data on a disk if
the data is stored as a series of dots on a shiny surface. The dots
are burned onto the disk using a laser ... and are read from the disk
also with a laser. Because these disks use laser light to read
and write to the disk they are often called optical disks.
Most optical disks can only be written to once and that
data cannot be deleted or written over the top. This type of disk
is called a WORM disk: Write Once
times. But mainly they are called CD-ROMs as they are a form of Read
Disks (or DVDs) are a type of
optical disk that is able to hold a lot of data (enough for an entire
Some optical disks can be written to many times: they
are more expensive. A common type of re-writable disk is the Minidisk:
used for recording music and computer data.
Answer these questions:
out of 10 on that test