Windows USB flaw drains batteries

Microsoft has confirmed the existence of a flaw in its USB 2.0 drivers for Windows XP Service Pack 2 that can cause a notebook to consume power at a faster-than-expected rate when using a peripheral device.

The issue, first uncovered by Tom's Hardware two weeks ago, appears to affect certain Intel-based notebooks running Windows XP Service Pack 2. When a peripheral device was connected to a USB 2.0 port, the notebook's battery life dropped at a greater rate than would normally be expected from the use of a peripheral such as a mouse or storage key. At the time that details of the flaw were published, Intel denied its processors or chipsets were the responsible for the issue. And Microsoft refused to confirm to ZDNet UK sister site CNET News.com until yesterday that the software company was responsible for the battery performance problem .

Microsoft published a Knowledge Base article on the subject in July 2005, but made that information available only to PC vendors and partners, a company representative said in a statement. The software maker is not releasing the article to the public, but a copy was posted on Slashdot that industry sources have confirmed was the original article.

In that article, Microsoft outlined a problem with its USB 2.0 drivers that prevents a mobile processor from entering advanced sleep states designed to minimise power consumption. On Tom's Hardware's testing, the effect was even more pronounced on Intel's new Core Duo processors, which are capable of entering a deeper sleep state than older Pentium M chips. Other tests by reviewers such as Anandtech found the problem affected notebooks with a variety of Intel processors. It was not clear whether the issue also affected notebooks with AMD's Turion or Athlon 64 processors.

In the private Knowledge Base article, Microsoft outlined a fix that involved modifying the registry key for USB 2.0. However, since then the company has realised that this is an impractical fix for most users, and is working on a new fix that could involve a BIOS update patch, a company representative said in a statement.

The severity of the problem depends on how USB 2.0 has been implemented in a notebook — which encompasses a wide variety of factors such as the operating system, processor, chipset, USB 2.0 device, and the software and drivers attached to all those components, an Intel representative said. Intel is also working on a fix for the problem that would not be dependent on a software download, such as a tweak to future processors, the representative said.

Notebook users who experience the problem should contact the manufacturer of the notebook for further assistance. Some notebook manufacturers have modified the registry keys as outlined in the Knowledge Base article, but this solution does not always work as intended outside of lab testing, the Microsoft representative said.