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Tablet PCs are mobile computers that run Windows XP Tablet PC Edition, a version of XP that features built-in handwriting recognition. The devices come in two general form factors. The pure slate design looks like an overgrown Pocket PC and doesn't have a keyboard (although all Tablet PCs can accept external USB keyboards). The convertible units are basically notebook PCs with a swiveling display that you can fold down to cover the keyboard. When the keyboard is covered or removed, you control the Tablet PC by using an electronic stylus that communicates with the display's built-in active digitizer.

The Tablet PCs in this Buyer's Guide expand on the basic form factors. Some of the listed products are as light as 2.2 pounds; others offer displays as large as 14.1" and processor speeds as fast as 1.6GHz. Tablet PC prices, however, remain somewhat higher than conventional notebook PC prices.

Both pure slate and convertible designs have advantages and disadvantages. Pure slate units are usually thinner and lighter than their convertible brethren, but propping up a pure slate Tablet PC in your lap or on an airline tray table isn't particularly convenient. The convertible form factor makes you carry the keyboard with you even when you don't need it but is easier to use on your lap or in a small space.

HP, Intermec, Motion Computing, NEC Solutions America, and Xplore Technologies make pure slate Tablet PCs; Acer makes convertibles. Fujitsu Computer Systems, Gateway, and ViewSonic make both pure slate and convertible designs, whereas HP and Motion Computing offer add-on keyboards that transform their pure slate Tablet PCs to convertibles.

All the Tablet PC vendors use Intel Pentium M processors (even HP, which used Transmeta's Crusoe processor in last year's Compaq Tablet PC TC1000). Most vendors also use Intel Centrino mobile technology. Intel claims that the combination of Centrino and Pentium M technologies provides a significant increase in battery life, although you'll probably still need a spare battery if you expect to use a Tablet PC on a coast-to-coast flight. Most Tablet PCs are optimized for weight rather than long battery life.

If you need a display that's viewable in the sunlight, you have a choice with this year's designs. Fujitsu's Stylistic ST5000 Tablet PC and Intermec's CT60 Rugged Tablet PC are available with reflective displays for outdoor use. The CT60 also features a one-piece vacuum-sealed aluminum housing that's designed to the MIL-STD-810F military standard. It competes with Xplore's iX104RD Renegade Dual Mode Tablet PC, a rugged unit that's designed and tested to survive a 4' drop onto a concrete floor. The iX104RD is also the first Tablet PC to accept both pen and touch input.

The OS that all these units run, XP Tablet PC, hasn't changed significantly in the past year (although it's gone through rounds of patches and hotfixes). XP Tablet PC includes all the XP Professional Edition features, plus handwriting-recognition and electronic-ink support. One Tablet PC-specific application—Windows Journal, which allows on-screen note taking—is built in. XP Tablet PC's pop-up input panel lets you use the stylus to input printed characters or cursive writing to text fields in any Windows application. You can also bring up an on-screen keyboard and use the stylus to tap letters one at a time.

Some XP Pro features are enhanced in XP Tablet PC. For instance, speech recognition is integrated into the same input panel that handwriting recognition uses. The speech-recognition feature works best with a headset and boom microphone.

Microsoft plans a major XP Tablet PC upgrade sometime this summer, when the company releases XP Service Pack 2 (SP2). The upgrade will offer handwriting-input improvements, along with XP SP2's security enhancements (including a built-in firewall that's on by default). I received a review copy of the enhanced Tablet PC OS as this article went to press. In an upcoming issue of Windows & .NET Magazine, I'll review the updated OS and tell you about its new features.