The commuter with a rolled-up screen

It is some time in the future. A commuter pulls a small computer out of his pocket and unrolls a screen from the top of it. He presses a button and a newspaper article appears.

The really clever technology here is not the electronic newspaper, but the roll-up screen on which it appears. It already exists, however, as one of the combatants in a battle that will decide the flat-screen technology of the future. At the Japan Electronics Show, held in Osaka in late October, three rival systems were on display as companies staked their claims for the multibillion-pound market. The takings for the winners will be vast, as wall-hanging televisions and slimline computer monitors, as well as portable devices such as electronic newspapers, become consumer essentials.

The cathode ray tube, used in most television sets, is more than 80 years old and is easily the best display technology when it comes to colour, brightness, contrast, resolution and price. But the CRT is also large, heavy and power-hungry. Little wonder that portable devices such as notebook computers and electronic organisers use other types of display systems.

The leading flat-screen technology is the liquid crystal display (LCD), first used in wristwatches and calculators, but now found in devices such as camcorders and notebook PCs. Sharp, the world's leading LCD producer, estimates that the global market for LCDs will be worth pounds 4bn in 1996. LCDs are small, thin, light and use little power. The best LCD screens are controlled by hundreds of thousands of transistors, which give very good picture quality. But these so-called active LCDs are difficult and expensive to produce - especially when the screen is larger than six inches across.

Isamu Washizuka, Sharp's senior executive director for LCD business, says that LCD prices are going down by 15 per cent per year, and that the yield rate (the number of fault-free LCD panels made during a production run) is "better than 50 per cent". Even so, large LCD screens are not cheap. Sharp markets a 14in LCD TV in Japan that costs around pounds 4,000. Samsung has produced a 22in LCD panel that took four years to develop and had a budget of pounds 13m. At Osaka, Sharp unveiled a 28in LCD prototype - the world's largest direct-view LCD screen. What is more, the company is developing a 42in version, due to be shown next year. Only lottery winners will be able to afford these, at least at first.

Sharp is also working on new forms of LCD screens. One of them is a plastic- based LCD that is flexible and could be used for an electronic newspaper; the idea would be to unroll the screen like a scroll. Sharp is also developing tougher LCDs that can withstand mechanical shock - anyone who has ever dropped a notebook PC and smashed the LCD screen will appreciate this development.

But other display systems are snapping at the heels of LCDs. One of these is the gas-plasma display. This works by passing an electrical current through a mixture of inert gases, which causes it to discharge and glow (a neon light uses the same principle). At the Electronics Show, Fujitsu, Panasonic, Pioneer and Mitsubishi were showing large plasma displays, some of which were 40in across. Supporters of plasma say that the technology is ideal for large screen displays. But on the downside, the picture quality is not as good as the best LCD systems.

A third system, which is a blend of LCD and plasma technologies, poses a more serious threat. The Plasma Addressed Liquid Crystal (PALC) system has been developed by Sony and the US electronics company Tektronix. PALC works in a similar way to conventional LCD displays, but with one crucial difference. Instead of controlling a display with thousands of transistors, PALC uses a plasma discharge. This makes it easier and cheaper to produce the displays, because unlike active LCDs, they do not have to be made under clean room conditions.

Sony's PALC sets, which will be marketed under the name of Plasmatron, are thin (around 4in deep) and wide (some versions will be up to 50in across). They will also be cheaper than other flat-screen systems, costing around twice the price of a conventional CRT set when they go on sale in Japan next year, Sony says.