Analysts say that's a good start, although the company is hoping to get the software installed on a billion devices over the next three years.

Microsoft, which is known for making software for personal computers, is hoping Windows 10 will help it rebuild loyalty among users who are increasingly relying on tablet, smartphones and other devices.

Microsoft is offering Windows 10 as a free download for many computer owners. It's also installed in new machines that are being sold this fall.

Along with some new features, Microsoft designed Windows 10 to fix some unpopular elements of the last Windows version.