All notebooks are portable, but the smaller, thinner and lighter they are, the more places you can take them. There’s a distinction between 13” thin and light machines like the Sony VAIO SZ and Fujitsu LifeBook S series, tiny sub-notebooks with tiny screens and cramped keyboard and true ultra-portables that weigh in at under 2 kg, can be just 30 mm thick and hardly ever have an optical drive. For portability these have 11” or 12” screens; we’re starting to see widescreen models like the Toshiba R400 which add a little size and weight, but even 12” models have good-sized keyboards. Expect a screen resolution of 1280 x 800 or 1366 x 768 for widescreen models.

After the screen the battery is the largest and heaviest component in a notebook, and keeping the size and weight down mean that typical battery life is 3 hours, or 6 with an extended battery (although HP is claiming a far longer battery life for the forthcoming Compaq 2710p Optimator and Sony claims up to 9 hours for the Sony VAIO TX3Xp). Look for an extended battery that works as a wrist rest or lifts the keyboard to a better typing angle as on the R400, rather than one that replaces the standard battery.

You’ll see a similar battery life on the ThinkPad X61, Portege R400 and Samsung Q45, which all weigh a under 2kg, and a sub-1kg machine like the Asus U1F. That’s because while they all have low-voltage processors the heavier machines have Core 2 Duos running at 1.4, 1.6, 1.8 or even 2 Ghz, but the Asus uses the 1.06 GHz Core Duo U2400 – and a LED backlight to keep power usage down.

Even with the cheaper ultra portables, you’re paying for the portability and getting mainstream or budget performance. It’s not just the processor; these machines have slower 1.8” hard drives to save space and integrated Intel GMA graphics.

The U1F costs £1,315 compared to £800 for the Q45 or the X61. The VAIO TX3XP has an LED backlight and a single core Core Solo U1400, and the DVD burner puts the price up to £1485. If you need a DVD burner in an even smaller size, the 10.6” widescreen means the Fujitsu Lifebook p7230 weighs less than 1.2 kg; the 1.2 GHz U1400 and 945GMS Express graphics happily run Vista Aero but they’re not what you might expect from a £1400 notebook. For the same price and 500 g more you can get the 12” Portege R400, which is an ultra-stylish tablet PC with Core Duo U2500 and GMA 950 graphics. And although it weighs a little more, the DVD burner and 1.8 GHz Core 2 Duo makes the Samsung Q45 excellent value.