Some 14 million people installed the Windows 10 operating system in the first 24 hours following its release, Microsoft has said, calling the response "overwhelmingly positive".
The company said its new operating system aimed at computers, mobile devices and other gadgets got off to a strong start toward its goal of reaching one billion devices.
"We're humbled and grateful to see the response to Windows 10," corporate vice president Yusuf Mehdi said in a blog post late on Thursday (local time).
"We have seen unprecedented demand for Windows 10, with reviews and customer feedback overwhelmingly positive around the globe."
The stakes are high for Microsoft as it pushes out the new operating system for both traditional computers and mobile devices such as tablets and smartphones.
Windows 10 - Microsoft skipped directly from Windows 8, which got a lacklustre response - is being offered as a free upgrade for most devices.
It will allow for voice, pen and gesture input, and in some cases biometric identification for improved security.
Mehdi said the company is rolling out the software in phases to make the transition easier.
"While we now have more than 14 million devices running Windows 10, we still have many more upgrades to go before we catch up to each of you that reserved your upgrade."
In one sour note, the chief executive of Mozilla, which makes the Firefox Web browser, complained that Windows 10 imposes the new Edge browser as the default option, overriding choices made by users.
"The update experience appears to have been designed to throw away the choice your customers have made about the internet experience they want, and replace it with the internet experience Microsoft wants them to have," Chris Beard said.