"We're seeing preliminary demand well above where we were with Windows 7, which is gratifying," Ballmer said at an event launching new Windows phones.
Windows 7 is the best-selling version of Windows so far, selling more than 670 million licenses in three years since release in 2009.
"Over the weekend we saw an incredible response around the globe to Windows 8 and the Microsoft Surface," said Ballmer, referring to Microsoft's first own-brand tablet, designed to challenge Apple Inc's iPad. He did not give out any sales figures.
On Friday, there were moderate lines at Microsoft's 60 or so stores across the United States for the Surface.
Ballmer was in San Francisco speaking at an event showcasing phones running its new Windows Phone 8 software, which go on sale this weekend.
Microsoft has struggled to make headway in the smartphone market, holding just 3.5 percent of the worldwide market, compared to 68 percent for Google Inc's Android devices and 17 percent for Apple's iPhone, according to tech research firm IDC.
The company highlighted how the new phones make use of Microsoft's SkyDrive cloud service, enabling users to sync and transfer music, documents and photos between PCs, tablets and the Xbox game console. Microsoft added that it now has 120,000 apps in its online store for phones, still far fewer than the number available for iPhone and Android users.
Ballmer and other Microsoft executives showed off slim and colorful phones from handset makers Nokia, Samsung and HTC.
The phones will be rolled out in the United States by carriers AT&T, Verizon Wireless and T-Mobile during November.
© Thomson Reuters 2012
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