Magnetic Tape

Magnetic tapes come in two forms:

	Tape reels - these are fairly large and are usually used to back up data from mainframe computers.
	Cassettes or cartridges - these are fairly small in size but able to hold enough data to back up the data held on a personal computer or a small network.


A magnetic tape cartridge	A magnetic tape reel

Because it takes a long time to back up onto magnetic tape, it is usually done at night or over a weekend when the computer network is not in heavy use.

Main advantages

	Relatively cheap
	Can hold in excess of 20GB of data (it is possible to get devices that will back up over 200 GB of data)
	Backup capacity is easily expanded by simply using more tape.

Main disadvantages

	Serial access - this means that in order to get to something on the tape, you have to go through everything that comes before it. Think of it like a video tape. The program that you want to watch might have been recorded half way through the tape, but you have to wind forward right from the start to get to it.
	Slow - Because of serial access, it is relatively slow to find the data that you need (however in an exam question, don't just say 'slow', compare it to a storage device with faster access.
	Specialist hardware is needed to read the tapes. Most standard PCs do not come with the hardware required to use them.
	Not suitable for heavy use - As you may realise from video tapes at home - they are a bit fragile with a tendency to stretch and tangle! Tape is best suited for back-up purposes.

Tape is a magnetic storage device