There must be a statistic somewhere that says how much the work we keep on the computer is worth. And still the school accounts, classwork and the complete dossier of the head of maths are at risk from third parties, fire and theft every day.

One statistic we do have is that after a serious loss of computer data, 70 per cent of businesses stop trading within two years. While it is unclear what the effect would be on the head of maths, it is clear that making back-up copies of work and storing it away is a habit that’s worth acquiring.

Most computers have software which will do a daily back-up automatically. You can set it to back up this week’s work and any files that have changed since last. Or if it’s the computer registration system you are protecting, you might back up twice a day and store the copies for a week, a month or whatever. Check the manuals for advice on how to run a fool-proof back-up plan.

There is a variety of storage technology available and it even includes the floppy disc. You can squeeze an entire book (about one megabyte of text) on to a floppy. But the “floppy-copying” quickly flounders when you want to back-up graphics and programs which need 10 or 100 times the space.

The next best is a tape drive or tape streamer. Costing from Pounds 80 to Pounds 200, they connect to the printer socket or fit inside the computer. They can store 250-800 megabytes (a full hard disc’s-worth) on a tape cassette costing just Pounds 15. A full back-up might take an hour, but the more expensive systems are faster.

If you need to back up a network you will want a serious device called a Digital Audio Tape drive. DAT is the technology that the industry intended to replace the audio cassette. It can store well over 2,000 megabytes on a Pounds 15 tape. Prices start at Pounds 500.

However, tape drives are really just for archiving work: you cannot normally run a program or get a file back quickly from a tape. And that’s where cartridge systems, like Iomega’s Zip Drive, come in. This new device gives you a 100-megabyte cartridge to store your work and it plugs into a printer socket or into the back of the computer.

You can keep the work of a whole year group on its own disc, or you can store those programs you use only occasionally. You can also use the Zip to upgrade an overloaded computer. The Zip Drive is slower than a hard disc but at under Pounds 150 and with cartridges costing around Pounds 15, it might even save a few computers from an early trip to the skip.

The Zip Drive is a derivative of the famous SyQuest a cartridge system which became a standard item in publishing. So if you’ve made up the school magazine and you need to take a huge PageMaker file to the printers, a SyQuest is what you might use. Schools also use them to back up software on a cartridge for transferring between machines. SyQuest works well with Apple machines as these have the necessary connection but you can get one which plugs into a PC’s printer socket. A built-in, 270-megabyte drive costs Pounds 280, an external one costs over Pounds 400 and a cartridge costs around Pounds 40.

The top cartridge systems are the optical drives. Fujitsu’s magneto-optical drive costs Pounds 500, but its 230-megabyte cartridges are just Pounds 20. Sony and Panasonic’s 1,000-megabyte drives cost Pounds 1,500 about the same as a CD-Rom writer. These writers are worth watching; you can cut your first CD with one and you have 650 megabytes of storage for only Pounds 6.

Somewhere in the middle of all this is Panasonic’s breakthrough PD system, now marketed by Cumana as the proTeus (see article below).

The key rule in storage is to keep your copies safe; that might mean sending them to a different building, a fire-safe or even off-site as supermarkets do. You can send your data down the phone lines to data storage companies like DataSafe. That might seem over the top but it avoids the need to tool up with back-up technology. DataSafe, which also provides the special software, says that work is password-protected and stored in two separate places and you can access it at any hour of the day.

Not since the bursting Filofax has so much precious information been trusted to one place. When we rely on computers so much, it’s bizarre that back-up storage is such a luxury extra. “Ahhm, has anyone seen my Filo . . . ?”.

Suppliers: * All figures given are typical high street prices. Most computer companies supply back-up systems.

* Datasafe, Secure Data International, PO Box 22, Letchworth, SG6 1QH. Tel: 01462 485859.

* Watford Electronics: 01582 487777.

* Hewlett-Packard: 01344 36936.

* Fujitsu: 0181 573 4444.

* Sony: 0181 784 1144.

* Panasonic: 01344 853508.

* Iomega: 0800 898563.