A Tablet-based ThinkPad has arrived, providing the first opportunity for sensible laptop users to adopt what has so far been a lame duck concept.

The X41, a lightweight convertible design, is the first Thinkpad Tablet, and the first product to be launched by Lenovo, the new Chinese owners of IBM's former laptop unit. The device is just light enough to count as an ultra-portable, and justify a high price with pen-based input and a twisting screen.

Qualification documents - and pictures - posted on the website of the US Federal Communications Commission (FCC) spoiled the announcement of the ThinkPad X41 Tablet, planned for the first day of Microsoft's Tech Ed conference in Orlando. As previously reported, the X41 is based on a convertible Tablet PC design, meaning it can be used as a regular notebook computer or as a tablet device.

The X41's 12.1-inch screen swivels to cover the keyboard when it is used in tablet mode. This convertible design has proved more popular than the slate Tablet PC design, which does not use a built-in keyboard.

Tablet PCs, though once lauded by Microsoft as the future of mobile computing, have so far been very poor sellers, despite products from names like HP, Toshiba and Acer. Some users love the ability to enter information using a digital pen, but the mass market has not been able to justify the extra expense of a Tablet PC.

The $1,899 starting price for the X41 is higher than the price of most notebooks but is around what other PC vendors charge for ultra-portable notebooks. The ultra-portable class of notebooks includes systems that weigh 3.5 pounds (1.6 kg), the same weight as the X41. Lenovo thinks that business that already have ultra-portable notebooks might be willing to switch over to Tablet PCs in the future once they realise they can get the ability to enter information with a pen for the same price as their current notebooks, Herman said.

The X41 uses Intel's Centrino technology, with low-voltage Pentium M processors and Intel's wireless chips. The base configuration includes the Ultra Low Voltage Pentium M 758 processor, 256MB of DDR2, a 20GB hard drive, and an integrated fingerprint reader. A $219 docking station is required to use CDs or DVDs.

Users can get their hands on the X41 from 14 June. It will also be available on Lenovo's and IBM's websites. Lenovo completed its acquisition of IBM's PC business in May.