Things are hotting up for anyone who fancies buying a pocket-sized palmtop 'personal digital assistant' (PDA) thanks to three recent developments. First, Palm Computing has licensed its award-winning Palm operating system (Palm OS) to recent startup HandSpring, so expanding the Palm platform to new and unusual machines. Second, Microsoft has learnt many lessons from its appalling Windows CE platform and come up with a much better palmtop-specific operating system to take its place, called PocketPC. And third, palmtops with colour screens are getting cheaper.

Palmtop PDAs are tiny handheld tablets with small touch-sensitive screens and no keyboard: you use a stylus to navigate the software and enter data. All palmtop PDAs offer some form of handwriting recognition which turns pen strokes into numbers and letters, or you can tap away at a tiny on-screen keyboard image.

The number of colour-screen palmtops is sharply on the increase. Colour screens shorten battery life, but battery technology is improving and you can normally expect between 6 and 12 hours of active use between recharges. Compare that with a typical mobile phone which usually peters out after a couple of hours of talk, and suddenly palmtops don't seem quite so poor. Longer-lasting mono-screen palmtops are still dominant because of price, but colour is an unstoppable trend just as it was with notebook PCs during the 1990s.

Here we take a look at five of the most popular PDAs on the market, based on Palm OS and Microsoft's PocketPC, three of which come with colour screens. Click the 'NEXT' link below to find out more.

Company: Casio

Contact: 020 8450 9131

Company: Palm

Contact: 020 7365 9820

Company: Hewlett Packard

Contact: 01344 360000

Company: Handspring

Contact: 020 8263 2847

Company: Palm

Contact: 020 7365 9820

Tags: palm os palm iii personal digital assistant pocket pc mobile phone palm inc microsoft windows iphone