That's more than the total install base of Windows' largest competitors, Gates quipped as he began his keynote at the Windows Hardware and Engineering Conference (WinHEC) here.
"As of last week, we've (sold) nearly 40 million copies," Gates said. "That's twice as fast as the adoption of Windows XP, the last major release we had."
Confirming news that had already leaked on its Web site, Microsoft also announced Windows Server 2008 as the official name of Windows Server "Longhorn," which is due to be finalized later this year.
In announcing the Windows Server 2008 moniker, Gates poked a little fun at his company's penchant for less-than-dynamic product names.
"We've been working hard thinking about it," Gates said. "We played around with a couple different ideas, but what we are going to go with is...Windows Server 2008. We know it's a surprise for us to pick something so straightforward."
Gates also announced several new partners for its Windows Home Server product, including Gateway and Medion. Microsoft has already said that HP will have home servers based on the technology later this year.
"This will come out in the fall," Gates said. He also said that smaller computer makers, known as system builders, will also be able to build products based on Windows Home Server. Microsoft has positioned the product as a central repository for media such as photos, movies and music as well as a more seamless way to back up PCs in the home.
Microsoft also announced the results of a study it commissioned IDC to do that found for every dollar Microsoft makes off Windows Vista and Windows Server 2008, other technology companies will take in an additional $18. IDC also found other companies will sell more than $120 billion in products and services around the two Microsoft operating systems.