Microsoft's new Windows 7 operating system boots slower than its unloved predecessor, Windows Vista, a PC tune-up developer said today.

The claims by iolo Technologies, a Los Angeles maker of PC software, contradict Microsoft's boasts that Windows 7 starts up faster than Vista.

According to iolo's tests, Windows 7 starts up 42 per cent slower than Vista -- one minute, 34 seconds versus one minute, six seconds -- on a brand new machine when the time trials are run to the point where the machine is usable, at least by iolo's standards.

Windows 7 does seem to start faster than Vista, said iolo, with its time-to-the-desktop measured as around 40 seconds. But iolo measured startup as the point where the computer is "fully usable," with a low load on the processor.

Microsoft has said it's dedicated significant resources to making Windows 7 boot, and resume from sleep and hibernation, faster than Vista, which has been panned since 2007 for starting slowly.

Other tests, however, have echoed iolo, and showed that in some cases Windows 7 does boot slower than Vista. PC World, a sister publication to Computerworld , for example, benchmarked the new operating system as starting about 10 per cent slower than Vista when 32-bit versions of the two were compared, although it was 14% faster on 64-bit.

iolo also said its tests indicated that Windows 7's startup times, like Vista's, degrade over time. After several "commonly-used" applications have been installed on a new Windows 7 box, for instance, its boot time -- again, as measured by the company -- slows to two minutes, 34 seconds, an increase of 64%.

Over an even more extended span, Windows 7's boot times get more sluggish than that: By the end of a simulated two-year period, Windows 7's startup times increased more than 330%.

Boot times have become a hot topic. Last week, Chinese computer maker Lenovo said its new ThinkPad notebooks and ThinkCentre desktops will boot Windows 7 56% faster than when loading XP or Vista, thanks to operating system, driver, and power management tweaks it made.

iolo said it will release more details and results of its Windows 7 boot-time benchmarks on Monday.