Microsoft is at it once again, claiming reliability and performance improvements for Vista. But it hasn't offered much concrete evidence to support those claims. According to Jim Allchin, co-president of the Windows platform group, "there's no question that Windows Vista is more reliable than any version of Windows ever shipped." He emphasizes the extensive testing Microsoft did (and it did release far more public betas than for any previous version of Windows). Allchin also points to automated stress testing that he says is twice as rigorous as previous tests with earlier Windows development efforts.

The question is, do the millions of Windows users who have been through version after version buy this? For reviewers, the problem of assessing performance and reliability boils down to this: It takes six months of real-world use, installing and uninstalling applications, running Web apps -- in short, living with the finished version of the new operating system -- to really know the truth about whether Vista truly is faster. Don't believe anyone who tells you they know otherwise. It's the only test that matters.

What we can tell you is this: When Vista is installed on a machine that fully supports the Aero interface (check the video requirements on this Microsoft page), whether real or perceived, the operating system opens files, folders, menus and dialogs faster than its predecessors. Application loading performance seems improved (especially on subsequent opens in a session), if not instantaneous. Windows shutdown times (not Sleep) are also noticeably faster, but will that still be the case six months from now? Windows cold boot times don't appear to be much improved at all.

Based on our empirical evidence derived through extensive usage of Vista through all the betas and technical previews up to the minute, we agree with Allchin. Since Windows Vista Beta 2, this version has been more stable than Windows 2000 and Windows XP, and at least as stable as the Windows Server 2003, whose core it is based on.

The one clear-cut performance improvement actually delivers reliability benefits too. Microsoft's new Sleep functionality actually works on most PCs, and it works quickly. (See for more about Sleep.)