Storage Media

Storage Media

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 off?

All these questions are related to the ways in which computers store data.

Paper Tape

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 to numbers.

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).

Paper Tape

Magnetic Tape

Magnetic Tape

The problem with paper tape was that it kept on breaking - since the more holes that you punched in it the more fragile it became.
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 unusable.

Floppy (magnetic) Disks

Hard Disks

Hard Disk

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.

Optical Disks

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 Read Many times. But mainly they are called CD-ROMs as they are a form of Read Only Memory.
Digital Versatile Disks (or DVDs) are a type of optical disk that is able to hold a lot of data (enough for an entire film).

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.

Optical Disks

Answer these questions:

  1. What does the word BIT stand for ?
  2. How many bits are there in a byte ?
  3. How are data bits represented on paper tape ?
  4. How are data bits represented on floppy disks ?
  5. What was the main problem with paper tape ?
  6. Why are disks a better shape for storing data than tapes ?
  7. How are data bits represented on a hard disk ?
  8. What does the acronym WORM stand for ?
  9. What is used to burn the data onto an optical disk ?
  10. What does DVD stand for ?


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