Surely there can be little new to say about photocopiers - you put the original document on the top, press a button, and a copy pops out of the side.

Modern copiers may possess more 'bells and whistles' than their predecessors, but have there really been any significant changes in photocopier technology since plain paper replaced coated paper in the 1970s?The answer is 'yes', for while the exterior of photocopiers has remained physically the same for many years, inside there has been a major development - the change from 'optical' to 'digital' copier technology.

The distinction, according to David Woodley of Kodak's office imaging division, is as follows.With an optical copier, which is the traditional type of photocopier with which most people are familiar, light is flashed onto the original.

This light is in turn reflected onto a light-sensitive film belt or drum (in smaller machines the drum is actually contained inside the removable toner cartridge, which explains why they are so expensive) giving it an electronic charge which is the equivalent of a photographic 'negative' of the shape of the original image.

Paper is then passed over the drum to receive an electronic charge which forms a 'positive' image of the original.

Oppositely charged toner, the 'ink', is attracted to the image area and 'fixed' to the paper by the copier's heated fuser rollers - those are the bits you burn yourself on when you try to clear a paper jam.However, in the digital copying process the image of the original is first 'scanned', rather like a fax, into an electronic form before printing.

The relevance of this intermediate stage is that it allows the image of the original to be manipulated before printing so that, for example, it is possible to get a better reproduction from a poor original, whereas with optical systems the copy can only be as good as the original.

It also means that originals which traditionally reproduce very poorly - eg half-tones like photographs - can be enhanced so none of the texture is lost.Over the last couple of years digital systems have started to come into their own as the demand for colour photocopiers has increased.

Indeed, some of the latest copiers from Rank Xerox and Kodak use a colour reproduction process standard called 'EFI Fiery' which can now reproduce copies of photographic quality.While not everybody needs colour, there remains an argument for employing digital copying in more modest applications where just black and white copies are required.

This is because with a digital system the original needs to be scanned only once before being reproduced any number of times, whereas with optical copiers the original has effectively to be scanned each time a copy is reproduced.The net result is that while digital copiers are more expensive than their optical brethren, they are also a lot faster.

Copier manufacturers reckon that organisations regularly making 20 or more copies from one original will find that digital copiers are now a more economic proposition than optical copiers.

Purely financial arguments may be a dangerous basis upon which to ground technology purchasing decisions, but there are other hardware factors that should be added into the equation.First, because the digital copier is basically a high speed, high quality printer of digital images, there is nothing in theory to stop it being linked to a PC or computer terminal to double as a printer of computer generated images; for example, for the output of desktop p ublishing (DTP) material, such as the marketing and promotional literature many solicitors' practices produce.

Indeed, a growing number of 'multi-functional devices' are now coming onto the market which, at different times of the day, can serve as copiers and printers, thus effectively doubling the utilisation of capital investment in the hardware.Second is the potential link between digital copiers and document management techniques.

Depending upon the type of system you have - and the more sophisticated the features, the more expensive the system - once you have scanned the image of the original into a digital copier, you can either print out any number of copies or retain it as a digital image until it is needed at some later date.

One of Kodak's new systems can produce copies of documents at a rate of 6600 an hour.

It can also file the scanned images and store them on compact disk - one CD can store over 10,000 pieces of A4 paper.All in all, the humble copier has come a long way.