Tablet PC makers are offering a variety of designs as they finally begin to ship products based on a pen-enabled version of Windows XP.

A flat-tablet format without a keyboard is favoured for Fujitsu Siemens' Stylistic ST4000, Research Machines' Tablet PC and ViewSonic's Tablet PCV1100. Acer's Travel-Mate C100 and the Portégé 3500 model from Toshiba, however, offer a clamshell notebook format with a screen that can swivel and lie flat against the keyboard - in what Microsoft describes as "slate" mode. Meanwhile HP, with its Compaq Tablet PC T1000, is the only vendor to offer a model that can be attached to a notebook base.

Tablet docking on models from Fujitsu Siemens and Compaq allow recharging and access to peripherals. The majority of devices have at least a 10.4in screen, the largest being Toshiba's at 12.1in. The first models weigh between 1.4kg and 1.8kg.

Most vendors use Intel's Pentium III processor but the Compaq TC1000 incorporates a 1GHz Transmeta Crusoe TM5800 chip, in an attempt to achieve a longer battery life. Battery life on the Pentium III-based Tablet PCs will be about three hours under normal conditions.

Tests conducted in IT Week Labs show that for systems running Windows XP and Tablet PC operating systems, 256MB of main memory is a minimum requirement. All the new Tablet PCs have this configuration as standard.

All also have integrated 802.11b wireless LAN adapters, but only Toshiba's Tablet PC offers Bluetooth wireless connectivity as standard.

The minimum hard disk size is 20GB and most models have a PC Card slot.

Some vendors are providing CompactFlash (CF) slots, and Toshiba's device houses a Secure Digital (SD) slot as well.

But although some PC makers, including HP, predict that Tablet PCs will enter the mainstream, others are not so certain. Research firm Gartner Dataquest said last week that it expects just 1.2 percent of all notebook PC shipments next year to be Tablet PCs. That would equate to about 425,000 units, according to Gartner.

"Tablet PCs will suit many industry applications that currently use pen-based tablets," suggested Gartner research director Ken Dulaney. "However, clumsy hardware designs, a price premium and a lack of application support will be barriers for most users."

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