As notebooks shrink, batteries must necessarily shrink with them, and that makes it tough to extend battery life. The small batteries in pioneering UMPCs like the Samsung Q1 and Fujitsu's recently-announced U810 are rated at 6 hours or so -- and as with all battery specs from vendors, that seems optimistic.

Manufacturers are tackling the power problem from all angles, says Paul Moore. "Previously everybody was looking for a better battery, and they didn't see what was under their noses: The answer is to build a computer that uses less battery, one that manages resources better."

Even standard technologies are going green. Intel's Centrino Pro is expected to dominate laptop designs through the early part of next year. Intel's roadmap for the Centrino Pro is as much about energy savings as it is about performance. The chip does several tricks to save power, including optional flash-memory caching called Turbo Memory, and independent power management for dual-core CPUs that can turn off a core when it's not needed. In the first half of next year Intel will move to power-thrifty 45-nanometer chip technology with the Penryn processor line, and later in the year the follow-on to the Centrino Pro, the Montevina platform, will further reduce power consumption.

AMD, which has been late to the mobile processor party, has several projects in the works that will result in lower power consumption, but most of them aren't expected until 2009. Next year it will ship a dual-core processor code-named Griffin, part of a notebook platform code-named Puma, the company's first design effort targeted exclusively at the notebook market.

Things will get much more interesting for AMD in 2010, when its Fusion chips are expected to come to market -- single-chip processors that merge a CPU (with up to four cores) and a graphics processor. AMD is also developing an ultra-low-power CPU architecture code-named Bobcat for mobile devices such as UMPCs and consumer electronics products. Bobcat will consume just one to 10 watts of power. But you'll have to wait until 2009.

Low-power x86 processors present an opportunity for other CPU makers as the market for UMPCs, smartphones, and digital TVs grows.

Intel will ship a new processor, code-named Silverthorne, for these devices in the first half of next year.

VIA Technologies, Inc. makes the C7-M Ultra Low Voltage processor that consumes as little 3.5 watts of power, and has released the Nanobook, a reference design for a UMPC built around this processor. In mid-August, the company announced an even lower-powered line of processors, the Eden ULV chips, which will run on as little as one watt.

Marvell is another major player in the low-power processor market. It bought Intel's XScale CPU line last fall, and an XScale processor drives the Palm Foleo.

(Incidentally, "green" doesn't just mean "low-power." Most PC manufacturers have pledged to eliminate toxic materials from their products and have launched recycling programs to reclaim old equipment.)