In the race to make ever lighter laptop computers, Toshiba is poised to take the lead in the 12-inch screen class with new models coming from June.

The Dynabook SS RX1, which will be sold elsewhere in the world as the Portege R500, is available in several configurations, the lightest of which is just 768 grams, Toshiba said Tuesday. That's more than 100 grams lighter than Sony's Vaio G laptop that was launched in late 2006 and had been regarded as the lightest in its class until now.

In the hand the new laptop feels impressively light and well balanced, unlike the Vaio G, which I found felt a little heavier towards the back of the machine than at the front.

Toshiba has obviously put a lot of work into the machine. The keyboard is just a few millimeters thick but the keys still travel enough that typing is comfortable.

There are also some nice design features. For example, the top half of the laptop with the screen is slightly smaller than the bottom half so the screen is better protected, according to Toshiba, if the laptop is dropped and lands on its side. The thickness of the magnesium body also differs to provide more protection where it's needed, the company said.

It's also thinner at the front than at the back where the hinges are - 19.5 millimeters versus 25.5 millimeters. That's so it's easier for business people to push the laptop into a shoulder bag, said Akitoshi Shiraga, group manager of Toshiba's laptop consumer product planning group in an interview.

And for people who are using the machine outside in direct sunlight, there's a conveniently located button just under the display that switches off the backlight to make the transreflective screen easier to read.

At the computer's heart lies a 1.06GHz Intel Core2 Duo processor. The screen has WXGA resolution (1,280 pixel by 800 pixel) and all models pack 802.11a/b/g Wi-Fi, an Ethernet port, 3x USB2.0 ports, iLink (IEEE1394), monitor socket, microphone socket and headphone jack.

US models (and, one hopes, the European ones) will also include support for 802.11n Wi-Fi, Toshiba said.

The lightest of the configurations - the one that weighs 768 grams - uses a 64 Gbyte solid-state disk (SSD) in place of a conventional hard-disk drive. SSDs use flash memory chips to record data and are therefore quieter, faster and more energy efficient than hard drives, which record data on a fast rotating magnetic disk.

Users can choose to replace the SSD with an 80 Gbyte or 120 Gbyte hard disk drive and add an optical drive to increase the machine's storage - and inevitably the machine weight. However a full-featured machine with hard disk, optical drive and six-cell long-life battery is still pretty light at around 1kg..

The long-life battery, which includes six cells and doesn't protrude beyond the edge of the machine, provides enough power for up to 12 and a half hours of use based on a Japanese industry benchmark, said Toshiba.

In Japan, the laptop will sell for about ¥225,000 (£928).

Toshiba's US and European business units will announce availability in their respective markets later.