It's odd, I see this story everywhere. Now even in CNN. But I still haven't seen a story that explains where the numbers came from and what they represent. For

It's odd, I see this story everywhere. Now even in CNN. But I still haven't seen a story that explains where the numbers came from and what they represent. For instance, is this worldwide or US only? Are all PC makers considered (large and small ones)? For instance, are Brazilian PC maker Positivo's sales considered? Some stories refer to "PCs with Windows" or "Microsoft's PCs". Does that mean they only count PCs bought with Windows preinstalled?