Upcoming versions of Transmeta's Efficeon chips will support the NX (No Execute) feature enabled by Microsoft's upcoming Windows XP Service Pack 2 release, but Intel's Pentium M processor - as used by most ultraportable and thin-and-light notebooks - will not support the NX feature until the first half of 2005, an Intel spokeswoman said.

NX is a security feature that blocks attempts by hackers to use buffer overflows in Windows XP to execute viruses or worms. Transmeta will update its current Efficeon processors with a new version of its code-morphing software to enable the technology, said John Heinlein, director of strategic partner initiatives at Transmeta.

Transmeta's processor architecture uses software to control many of the same tasks that are done with hardware components in other chips. This reduces the amount of power consumed by the Transmeta chips, but earlier versions of the architecture did not perform as well as the competition. Efficeon consumes anywhere from seven watts to 12 watts, depending on the application, and is found in extremely lightweight notebooks and blade PCs from companies like Sharp and HP.

Intel and AMD will support NX with some of their processors after the release of Windows XP Service Pack 2, which is expected in the fourth quarter. Intel's Itanium and Prescott Pentium 4 processors and AMD's Opteron and Athlon 64 processors have built-in hardware support for the features, but require the software support in Service Pack 2 to enable the NX technology.

Intel built the NX technology into its Prescott core, but disabled the technology until Microsoft released Service Pack 2, said Intel President and COO Paul Otellini at a financial analyst meeting last week.

However, it has not built that technology into the Dothan core, or the latest version of the Pentium M released earlier this month, an Intel spokeswoman said. Intel can either design a new version of that core or add the NX functionality to future Dothan processors in a new stepping, she said. A stepping is an incremental hardware update to a processor that adds new features or components.

The spokeswoman declined to comment on whether NX functionality would appear before Yonah, the code name for Intel's first dual-core mobile processor expected in 2005, according to sources.

Earlier this month, AMD released two Mobile Athlon 64 processors for thin and light notebooks that support NX, or what AMD calls Enhanced Virus Protection. Those processors consume more power than Efficeon, and are not designed for the same ultraportable notebooks that Efficeon targets, Heinlein said.