For Windows 10, Microsoft is aiming for a 10-digit installed base.
That's a 1 followed by 9 zeroes: 1,000,000,000. One billion devices running Windows 10.
At the Build developers' conference in San Francisco earlier this month, Microsoft's Terry Myerson declared that the company's goal was to reach the billion-device milestone "within two to three years after launch."
Now a billion might not be what it used to be, but it's still a big number. How realistic is it?
If you do the math, it's not hard to get to that number and even beyond.
That math is, unfortunately, fuzzy, because we don't really know how many PCs and tablets and phones are out there to a fine level of precision, nor what the owners of those devices have done with them since they were purchased.
But there are enough reliable sales figures out there, some in official reports from companies, others supplied by trustworthy market research firms, to make some educated guesses. Even with wide-ranging assumptions and allowing very broad margins of error, there are plausible paths to a billion.
With those caveats, let's survey the Windows 10 landscape as it might look in 2018.