The good news about Windows 7 is that it's faster than its predecessor, Vista. The bad news about Microsoft's new operating system, which went on sale yesterday, is that it is slower than Vista.

The contradictory statements only serve to show the confusion of numbers coming from technical analysts and publications about Windows 7 performance.

The US edition of PC World magazine ran Windows 7 speed tests on a range of computers doing a variety of tasks and was unable to declare it significantly faster than the much-maligned Vista.

Windows 7 "makes some performance strides over Vista, though in some cases we saw no clear-cut winner, and in one area Windows 7 lagged considerably behind its predecessor", the magazine said last month. Overall, Windows 7 was only slightly quicker than Vista - an improvement, nonetheless.

Meanwhile, over at PC World's IDG stable mate, Computerworld US, Los Angeles software developer iolo technologies is reported as having timed Windows 7 starting up 42 per cent slower than Vista on a brand new machine.

The new operating system might appear to boot up more quickly than Vista, iolo says, but the time taken until the computer is fully usable - with a low load on the processor - was 1 minute 34 seconds for Windows 7 versus 1 minute 6 seconds for Vista.

What's worse, it got slower at starting up as time went on, according to iolo, which bills itself as a PC tune-up specialist.

If that's embarrassing for Microsoft after the panning Vista received for its perceived sluggishness, the company's not letting on. In its performance claims for Windows 7, Microsoft avoids saying boot-up is quicker, while claiming it is speedier at going into and out of hibernation mode.

Ben Green, head of Microsoft's New Zealand Windows group, says the Windows 7 design emphasis has been on overall performance, which means "different things to different people".

"We've put a lot of time and effort into the performance as it relates to common use scenarios," he says, such as switching between applications and search.

And contrary to the iolo and PC World test results, Green reports users of pre-release versions of the OS are "very pleased" at the start-up speed.

It's true that there are all kinds of qualifications to any speed test. For a start, there are 32-bit and 64-bit versions of both operating systems, and PC World's testing showed 64-bit Windows 7 started faster than 64-bit Vista.