San Francisco - Microsoft chief executive Steve Ballmer on Tuesday said the Windows 8 operating system was off to a "stunning" start with four million upgrades downloaded since its release on 26 October.
"In just the last three days, we have sold four million Windows 8 upgrades," Ballmer said while kicking off a BUILD Conference for developers at the software giant's headquarters in Redmond, Washington.
"The level of embrace from enthusiasts is very, very high."
Ballmer added that tens many businesses have also switched to the latest version of Windows.
Analysts have depicted Windows 8 as a bold bet for Microsoft since it dramatically changed the long-familiar user interface to adapt to touch-screen mobile devices increasingly popular in modern lifestyles.
"The level of enthusiasm seen for the new products has really been stunning," Ballmer told the thousands of developers at the sold-out event.
Globally popular one-to-many text messaging service Twitter and online file sharing hit Dropbox are among applications being tailored to Windows 8, Ballmer told third-pary software developers at the gathering.
Microsoft kicked off sales of its revamped Windows 8 system and Surface tablet on Friday as it ramped up efforts to compete in a market shifting rapidly from PCs to mobile devices.