But during the announcement Microsoft executives said that Windows 10 will run on devices with screen sizes ranging from four to 80 inches, raising an important question: is "Windows 10" replacing "Windows Phone?"
And the answer, given during the Q&A portion of Microsoft's Windows 10 announcement, is a resounding "yes."
This shift was signaled earlier in September when Microsoft documents describing a gradual phasing-out of Windows Phone and Nokia branding was leaked online.
Microsoft wants Windows 10 to cover a huge range of devices and be the only operating system its users need.
"Our new Windows must be built from the group up for a mobile-first cloud-first world," Microsoft Executive Vice President of Operating Systems Terry Myerson said during the Windows 10 reveal.
Microsoft may have forgotten how to count, but at least its message with Windows 10 is clear.