3. Ultra-small

Motion Computing has an 8" Tablet PC - the LS800 is the size and weight (just 2.2 lbs) of a paperback book. Like UMPCs, this is too small to use like a normal notebook; although you can connect a keyboard and mouse, you need a table to do it and the screen size limits what you can work on. But for taking notes in meetings, browsing the Web and reviewing documents, it's a perfect portable that you'll never leave behind because you can't fit it in your bag.

Motion's tiny tablet is like a pad of paper - but you can plug in mouse, keyboard and optical drive to work at a desk.

The active digitizer makes the LS800 a real Tablet PC; UMPCs use a passive touch screen that you can work with a finger rather than a special pen. UMPCs use a passive touch screen that you can work with a finger rather than a special pen. This is very convenient on the move. But even though the Windows XP Touch Pack includes settings that do reasonably well at distinguishing between your finger tapping on a button and the side of your hand brushing across the screen, it's nowhere near as smooth as using an active digitizer. The first combination active and passive screens will reach the market in 2007; Lenovo's X60 will probably be the first portable to offer a screen you can write on smoothly with the standard tablet pen or tap with a finger to open a menu or select a button when you don't want to get the pen out.

The Sony UX Micro PC is like a PDA running Windows, complete with a slide-out keyboard.

With PDA-size devices like the OQO or VAIO UX, you still get a full version of Windows and standard applications but the screen and keyboard will be small, so the experience is more like using a PDA than a notebook. Often the keyboard slides away under the screen and you have to hold the device in both hands to type rather than resting it on your knee or on a table. Look for USB and VGA connectors so you can at least plug in a normal keyboard, mouse and screen when you're working at a desk.