Beginning in April, Google will patch and upgrade the desktop version of Chrome only on Windows 7, Windows 8, Windows 8.1, Windows 10, OS X Mavericks, OS X Yosemite and OS X El Capitan.
Chrome's desertion of Windows XP was expected -- in fact, Google had previously pegged the end of this year as the retirement timeline -- but the abandonment of Vista and the three OS X editions had not been hinted at earlier.
Google likely believed purging the still-supported Vista was a no-brainer because of its low user share, a Net Applications estimate that serves as a proxy for the portion of the world's desktop and notebook personal computers that run a specific OS. In October, Vista's user share was just 2% of all Windows-equipped machines.
Mozilla's Firefox browser supports all the operating systems that Chrome will leave in the ditch, and so will become -- assuming Mozilla doesn't mimic Google before April -- the best option for most of those left behind by Chrome.
Mozilla is typically the most cautious of the top four browser makers in pulling support. It didn't retire Firefox on Windows 2000, for example, until April 2012, more than a dozen years after its debut and nearly two years after Microsoft stopped updating the once-widely-used OS.
Chrome has been on a remarkable run since the beginning of 2015, accumulating 8.5 percentage points in user share since Jan. 1. That represented an increase of more than a third. In October, Chrome's user share stood at 31.1%, a record.
So while Google's decision to end support for the five operating systems next year may dampen growth as OS laggards move on to, say, Firefox, the impact will probably be minor because of Chrome's strong position. If the kill switch had been thrown now, not slated for April, Google's browser would face a maximum downturn of 4.5 percentage points if all Chrome users on Windows XP, Vista, and OS X Snow Leopard, Lion and Mountain Lion, suddenly deserted the browser. That's very unlikely: Those users are probably as indifferent to using an obsolete browser as they are to running an outdated OS.
Although a decline of that magnitude would be an embarrassing reverse for Google, it would not unseat Chrome from its second-place spot in the browser standings.
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