Bill Gates has revealed that Microsoft has shipped 40 million copies of Windows Vista, more than double the number of XP copies shipped in its first 100 days.

Speaking at Microsoft's Windows Hardware Engineering Conference (WinHEC), he said: "the reaction has been very strong. We thought Vista would open up a new level of ambition, and that is happening," he told the gathered hardware partners.

Microsoft had previously said that it had sold 20 million copies of Windows Vista in its first month after its consumer launch in late January. That, it claimed, doubled the pace of Windows XP, which sold 17 million copies after the first two months of launch in late 2001.

In an interview last Friday, Kevin Kutz, a director in the Windows client division, said Microsoft's sales figures include copies of Vista shipped to retail shops, licences ordered by hardware makers for pre-installation on PCs, as well as coupons given to customers for free Vista upgrades if they bought a Windows PC in late October or afterward.

Kutz did not disclose how much that last factor contributed to Microsoft's Vista sales. He denied suggestions that Microsoft's calculation method was designed to make Vista sales look better.

"We tried to be as absolutely consistent as we could," he said.

Kutz also denied that Microsoft was covertly offering incentives to partners to order as many Vista licences as early as possible, or otherwise engaging in "channel stuffing”.

"Market momentum is strong, and consumer response is good," he said.

In terms of the future, Gates said by 2008 all servers, desktops and devices would provide a 64bit processing environment.

"What does this mean for the industry," Gates asked. "It allows us to have lots of memory," including advanced visual and business intelligence."

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