Microsoft execs have drawn a line in the sand, predicting that Windows 10 will be installed on 1 billion devices within two to three years.

Terry Myerson, the head of Microsoft's Operating Systems Group, went public with that ambitious claim during the first day of the company's Build 2015 developer conference in San Francisco.

The 1 billion figure encompasses all kinds of devices that will be able to run the OS in some flavor, including desktops, PCs, laptops, tablets, Windows Phones, Xbox One gaming consoles, Surface Hub conferencing systems, HoloLens augmented reality glasses and various Internet of Things (IoT) devices.

Microsoft is developing Windows 10 so that it has a common core, a single store and a more unified set of development tools and programming interfaces, enabling the guts of the operating system to run on all these different form factors.

Microsoft is doing a lot to try to convince Windows users that it will benefit them to upgrade early and quickly to Windows 10. Microsoft execs have said they'll make Windows 10 free to Windows 7 and Windows 8 consumers(and some small business customers) the first year that the OS is commercially available. Microsoft also has made Windows 10 available for "zero dollars" and/or for a substantially reduced rate to its PC and phone partners in order to get more of them to bundle the OS with their hardware.

Making Windows 10 more appealing to business users who skipped Windows 8 because its UI and touch-first focus made it less appealing to customers relying on keyboards and mice -- and who didn't want to incur hefty retraining costs -- is a big priority at Microsoft. It should be, given Windows 7, and even the no-longer-supported Windows XP both have more market share than Windows 8.

There are currently an estimated 1.5 billion or so PCs running some version of Windows worldwide.

Updated: As a few readers have noted, this 1 billion by summer 2018 means we won't see a Windows 11, 12 or whatever, coming out any time in the next couple years. Yes, that shouldn't be surprising to folks who understand what "Windows as a Service" means. Microsoft plans to continue to push updates -- some minor and some major -- to Windows 10 for the foreseeable future.