SEATTLE - Microsoft Corp.'s Windows XP operating system is about to get faster and Windows Vista isn't, according to a report that caused a stir online this week as industry watchers speculated that a zippier XP could keep customers from upgrading to Vista.

(MSNBC is a joint Microsoft - NBC Universal venture.)

Microsoft, however, said it's too early to evaluate the two service packs it plans to release next year.

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Early versions are already in the hands of testers like Devil Mountain Software Inc., which helps big financial services companies track trading-floor computer performance.

Wellington, Fla.-based Devil Mountain Software ran several versions of XP and Vista through a test simulating common desktop computing tasks. It found the original Vista performed 50 percent to 100 percent slower than the prevalent XP Service Pack 2, or SP2.

Vista SP1, due out in the first quarter of 2008, barely improved the operating system's performance.

But XP SP3, scheduled for the first half of 2008, did improve on XP's earlier performance, running 10 percent faster than SP2.

That's a strike against Vista for IT professionals on the fence about switching, according to Craig Barth, the company's chief technology officer.

Kevin Kutz, director of Microsoft's Windows Client group, said the company is working on speeding up tasks like moving files between PCs, but it's a work in progress.

Michael Cherry, an analyst for research group Directions on Microsoft, said it's impossible to say if Microsoft has started tuning Vista SP1 for speed. Even if XP gets faster, consumers and businesses may still switch to Vista.

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"It might be an acceptable thing to me if it were slightly slower but more stable," Cherry said.

Benjamin Gray, an analyst for Forrester Research, said businesses will upgrade to Vista regardless, to "stay current with Microsoft's support life cycle."