A mysterious problem affecting certain high-speed systems running Windows Me and possibly Windows 98 could cause data loss at shutdown, PC Advisor’s sister title has learned.

Microsoft insists that the problem doesn't relate to its operating systems but has nonetheless released patches to address the problem.

During testing by PC World magazine – the US version of PC Advisor - of new high-speed systems this week, a vendor alerted the publication to Microsoft's warning of possible disk corruption occurring at shutdown on systems running 933 MHz and faster CPUs (from either Intel or AMD).

The problem occurs only in very specific circumstances, apparently involving ATA100 hard disk drives with large physical caches.

According to Microsoft, the very fast systems sometimes power down before the contents of the large drive cache have been completely written to disk. In other words, the system shuts down before the OS can save what you were working on.

The vendor, which asks not to be named, says the problem had shown up only on new systems running the recently released Windows Millennium Edition. However, Microsoft says the shutdown issue could surface on Windows 98 systems, as well.

"It's not specific to any operating system but has to do with larger hard drive caches in combination with fast processors," says Greg Sullivan, lead product manager of Microsoft Windows Millennium Edition.

Microsoft on Thursday sent patches for both Windows 98 SE and Windows Me to vendors with systems at 933 MHz and higher.

While insisting the problem was not related to any specific OS, Microsoft acknowledges systems running Windows 2000 are not affected because that OS has a different shutdown architecture.

"We've done work in Windows 2000 to address this and prevent it from happening," Sullivan says.