2. The Size Factor

There's no official definition of ultraportable, so check the size and weight along with the rest of the specs. Lenovo calls the V100 an ultraportable but because of the 12" widescreen, it clocks in at 4.1 lbs before you add an extra battery. You get a Core 2 Duo processor with the famous ThinkPad keyboard, built-in DVD drive, stereo speakers and an optional integrated camera so there's a good reason for the weight, but it is the heavy end of lightweight.

The spec of the HP NC2400 is close to that of the Lenovo V100, but its weight is much less.

Apart from choosing a Core Solo processor instead, HP packs a similar spec into the 12" widescreen NC2400 but that only weighs 2.8 lbs when you pull out the DVD burner or 3.6 lbs with the burner and a six-hour battery. That also beats Sony's 2.8-lb VAIO TX, which is only 11". Lenovo manages 2.6 lbs for the X60. If you want something a lot lighter you're looking at a slate Tablet PC or a sub-notebook; the Fujitsu-Siemens LifeBook P1510 is 2.2 lbs and the Sony VAIO UX is just 1.2 lbs.

You're more likely to take an ultra-light PC around with you, which means it needs to cope with traveling, being used outdoors and on trains and planes and other stresses a desktop or a heftier notebook doesn't usually face. While HP has one rugged Tablet PC that you can safely drop off the table onto a concrete floor, Panasonic specializes in rugged ultraportables that can take the pace. These are 2.7- to 3- lb aluminum notebooks with 11-15 hour battery lives that use heat pipes rather than fans so they're completely sealed and waterproof. The Toughbook CF-W5 has a flip-up DVD burner in front of the keyboard, the CF-T5 has a touch screen and a handle built into the case and the CF-Y5 is the heaviest but still weighs in at only 3.5 lbs with a 14" screen.

Several manufacturers of more standard portables use carbon fiber, magnesium or aluminum cases to get the strength without extra weight; just because they're small doesn't mean ultranotebooks have to be flimsy.

It's the screen that dictates the size and weight of a device. Sizes vary from 13.3" in the Sony VAOI SZ down to 9" for subnotebooks, 7" for UMPCs and 5" for pocket-size PCs but 11" and 12" are common for ultraportables. Resolution can make more of a difference; the Sony VAIO TX has an impressive 1,366x768, but 1280x768 or 1024x768 is more common. A widescreen adds a little weight and means you get a wider case to fit into your bag - but you also get a full-width keyboard. Many ultraportables have narrow keyboards, which may mean slightly smaller keys than you're used to on a notebook and fewer keys as well; the Portege R200 is unusual in having dedicated Page Up and Page Down keys as they're usually secondary functions on the arrow keys.

Slates like the Fujitsu Siemens Stylistic are very thin and light for the screen size.

Ultra-portables have the standard mix of pointing devices, usually touch pads and trackpoints, but there are some more unusual options. Tablets usually have rocker switches for scrolling, Sony VAIOs have jog dials and Lenovo has put a four-way controller on the X60. Motion Computing lets you scroll using the fingerprint sensor on its Tablet PCs (and most notebooks with a fingerprint sensor let you swipe your finger instead of typing in a password). The pen on a tablet controls the mouse pointer and also lets you write rather than type. Think about where you plan to work with your ultraportable; if you're not going to be sitting down all the time, an alternative input or pointing device will be easier to use than a keyboard.

Think outside this case; accessories like this combination fabric cover and keyboard from Eleksen for UMPCs like the Samsung Q1 make them more usable but not less portable.