Palmtop devices perform many tasks normally carried out on laptops, says Stephen Pritchard
The laptop is an essential executive accessory, but the best models strain both your back and wallet. Simple tasks, such as filling in an expenses claim or checking e-mail, hardly need Pentium processors. But manufacturers that designed highly compact laptop PCs found they were not commercial successes.

Olivetti built the Quaderno, a 386-based PC about half the size of an A4 pad. The Quaderno ran Windows, but it had a mono screen and small, keys.

Hewlett-Packard also tried the super lightweight with its Omnibook range. The Omnibook sacrificed power-hungry parts, such as the hard drive, in favour of data cards. It sold well to journalists, who liked its huge battery life, but other users wanted hard disks and colour. The Omnibook is now a mainstream laptop - the Quaderno is no longer made.

Fortunately for travellers, there are good products, below the level of laptops, that handle e-mail and word processing, and run for weeks on ordinary batteries.

The best known is the Series 3 from the British firm Psion. The latest version, the 3c, adds vital functions such as infra-red links to other computers and printers, optional Internet access and support for PCMCIA (credit card-sized) modems, and mobile phone adaptors.

The Psion comes with built-in software including a word processor and spreadsheet; the Psion's files work with Windows or a Mac. It is the most powerful and versatile of palmtop computers.

A different approach is adopted by Apple, with its Newton. The Newton is like an electronic note-pad: you write on a touch-sensitive screen with a special pen. The device currently on sale goes by the name of the MessagePad 130.

The MessagePad is slightly larger than the Psion. Its built-in software is less sophisticated, but more graphical. There's an address book, diary, and notes facility.

The most radical feature of Newtons is their handwriting recognition. A quick note can be left on the screen "as is", but the MessagePad can also convert it to printed text.

The technology is not instant: the computer learns to read the user's writing over time. With practice, though, the system can be accurate, if a little slow. For this reason, Apple makes a small keyboard that plugs into the MessagePad.

The MessagePad also differs from the Psion in its communications. Fax software is built in, as is a PCMCIA slot for modems and cellular cards; it has infra-red, too. Fax software is optional on the Psion, but standard on the Newton and should be plug and play with a PC card. The Psion needs an additional external card reader to work with a card modem. Apple's Internet software, however, is more restrictive. Currently, the MessagePad only works with CompuServe accounts.

Other firms are entering the market. Nokia has its own computer with built-in mobile phone, the Communicator; Hewlett-Packard has its Omnigo range, while Sharp has the Zaurus. This combines some of the features of both the Newton and the Psion, with a pen-driven touch screen, and a keyboard for typing. The Zaurus has CompuServe software built in for Internet access.

Any of these computers can do perhaps three-quarters of what people really use their laptops for, they are much lighter, and all cost under pounds 500. The most important difference between the palmtops is the way they handle communications.

All have additional applications, but the Psion has the most eclectic range: Psion users can even buy trainspotting software.