Stephen Pritchard opens a three-page special report on portable computers with a look at where the latest technology is taking laptops
Laptops are one of the fastest-growing types of computer. The research organisation Dataquest predicts that laptop sales will grow by more than 20 per cent this year. This comes at a time when most leading manufacturers have found it harder to sell desktop PCs, especially to businesses.

One reason for the portable computer's popularity is, undoubtedly, our changing lifestyles. More people are "hot-desking", "mobile" or "flexible" workers who spend far more time out of the office than back in corporate HQ. People with more conventional working patterns are turning to laptops to make presentations or to take work home. According to Apple, computer firms in Japan are buying laptop PCs simply to save on desk space.

These moves would probably be resisted, were it not for one key factor: laptops really are getting better. Computers are always a compromise between price and performance, and this compromise is even more acute with laptops, where weight and power consumption also need to be taken into account. In the past 12 to 18 months, there have been significant developments in processor power, multimedia capabilities, battery technology and, especially, portable screens. Modern laptops are easily capable of running the most demanding business applications, even if, function by function, they continue to cost more than their desktop equivalents.

The good news is that improvements will continue. Intel, which makes the processor chip used in most portable computers, is reducing the delay between the launch of its desktop central processing units (CPUs) and the low-voltage, portable equivalents, so laptops will become faster. Hard disks will become larger, and prices for the main memory (Ram) should fall as manufacturers switch to memory-hungry operating systems such as Windows 95 or Windows NT. Battery life probably won't advance much beyond the current, 3-31/2hours (provided by Lithium Ion technology) for at least the next couple of years.

Screens are the area where computer companies expect to see the most growth. The current generation of thin-film transistor (TFT) screens, sometimes called active matrix, are capable of displaying thousands of colours at a resolution of 800 x 600 pixels (equivalent to a 15in desktop screen). Laptop screens are now on the market at 11.8in for TFT, and 11.3in for the cheaper DST screens, although budget models will continue to be built with 10.4in displays for a while yet.

The next generation of computers will offer even larger, XGA standard monitors, to the point where there will be little difference between a desktop and a laptop display, especially as users sit closer to the screens on their laptops. "VGA is dead and gone," says Steve Crawley, portables product manufacturer at AST Computer.

"All the big manufacturers are moving to 11.3in, and 12.1in and 12.3in are starting to come on stream," he says. Samsung is even sampling a 14.2 in screen.

A better choice of screen sizes will bring in a wider choice of computers. The notebook computer is generally built around the dimensions of an A4 pad, so it sits, portrait format, in a briefcase. In some ways this was an artificial restriction, as a machine that was any larger would just be putting plastic around its 9in (or even 7in) screen. Larger displays will give designers the option of making a bigger computer, especially for the "desktop replacement" market: computers for people who have just one portable PC.

Leading manufacturers, including Compaq and Toshiba, predict a more fragmented laptop market. Not everyone needs, wants, or can afford a 14in screen, so manufacturers are looking again at the sub-notebook class.

Sub-notebooks were tried a couple of years ago, but they failed to sell as well as their larger and more powerful cousins. Now manufacturers are looking at the market again, partly because they expect mainstream laptops to become bigger, and partly because technology means a small computer can still be powerful.

Most manufacturers still feel constrained by the size of the keyboard, so there is, effectively, still a minimum size. IBM developed a Thinkpad with a "butterfly" keyboard that folded out to full size, but this has not spread to other designs. Even so, miniaturisation is bringing thinner and lighter computers. Compaq's latest Armada model, for example, is a touch under 11/2in thick.

Demand for smaller computers is driven, in part, by the need for executives to access their corporate computer networks and e-mail - or the Internet - on the move. They also want "go-anywhere" computers that can act as electronic diaries and address books. Apple and IBM are working on a very small laptop for the Japanese market with this in mind.

The new generation of truly mobile computers is not cheap, however. Compaq's slimline Armada is in the middle of its range, as are Toshiba's Portege and Apple's Duo, one of the last remaining true sub-notebooks. All leave little change from pounds 2,000, without extras.

This is why the third distinct product will be the budget laptop. Features such as expansion bays, multimedia support and CD-Rom drives, and larger screens have all added to the price of the standard, executive model laptop. This risks driving away the large numbers of potential buyers who may not need the latest technologies.

People who already have a powerful desktop computer and see a laptop as a second machine might prefer a slower chip or a smaller screen and price ticket. Compaq, Toshiba, IBM and Apple all have entry level laptops costing less than pounds 1,500, which are still capable machines.

Manufacturers expect the most immediate developments in laptops to be incremental: slightly faster chips, slightly better battery life, slightly thinner and lighter designs. This reflects a reaction by buyers against products that changed totally every six months. As Alan Rogers, laptop product manager at Olivetti, points out: "The market is maturing and has matured a lot over the past 18 months."

Real breakthroughs in design will have to wait for the next leap in technology. One could be lithium polymer batteries, which can be moulded into the computer's case and give rise to a variety of new shapes. Another is larger screens, as anything above 14in is too big for the standard A4 design and may prompt designers to look again at alternatives to the clam-shell design where the screen folds to cover the keyboard.

But by then, the keyboard itself might be an optional extra. Research laboratories are making progress on handwriting and speech recognition, helped by faster chips.

Ditching the keyboard should mean an end to the rule that you can have any shape of laptop you like, as long as it's A4.