Before Windows Phone 7 was even an embryo of a concept, Windows Mobile was king: It powered nearly half of smartphones in use, a led the industry in features. Then, in 2007, things started to go wrong. Very, very wrong.

Silicon Alley Insider has charted Windows Mobile's platform share, which is to say the proportion of users who were using it at a given time, over the last four years. For showing decline, figures like these are more telling than sales—they mean that, for years now, people haven't been buying Windows Mobile phones nearly as fast as they've been ditching them.

More interesting than what it shows is what it projects: Windows Mobile 6.x phones have been collectively kneecapped by Microsoft's announcement yesterday, and rendered spectacularly unbuyable outside of enterprise circles. In other words, that line—the one that dragged down past RIM in 2008, and that dropped past Apple last year—is going to keep plunging for the rest of this year, until Windows Phone 7 tries to haul it back up. And until then, it's only going to get steeper. [Silicon Alley Insider]