Apple yesterday gave its strongest signal yet that it will continue to support OS X Snow Leopard with patches for the foreseeable future rather than retire the still-active operating system.
On Thursday, Apple shipped Security Update 2013-001, which patched 11 vulnerabilities in the client and server versions of OS X 10.6, better known as Snow Leopard.
That update was notable because it set a record for Apple.
Historically, Apple has patched only the OS X editions designated as "n" and "n-1" -- where "n" is the newest available -- and discarded support for "n-2" either before the launch of "n" or immediately after.
(In this scenario, Snow Leopard is "n-2," since it was followed by Lion in 2011 ("n-1") and then Mountain Lion in 2012 ("n").
Snow Leopard's patches of yesterday -- eight months after Mountain Lion's launch -- were a record, easily breaking the previous set by OS X 10.1, or Puma, which received its final patches three months after the debut of 2003's 10.3, or Jaguar.
None of this would be noteworthy if Apple, like Microsoft, clearly spelled out its operating system support policies. But Apple doesn't, leaving users guessing about when their current Macs will drop into the unsupported dustbin.
The causes of Apple's longer-than-usual support for Snow Leopard are just as mysterious -- Apple habitually declines to comment about anything related to security -- but analysts and experts have tapped a pair of reasons.
One is the accelerated release schedule Apple's adopted, and has promised to continue, that resulted in back-to-back upgrades in the summer of 2011 (Lion) and 2012 (Mountain Lion). The shorter span between editions means that unless Apple extended its usual support lifecycle, Snow Leopard would have fallen off the list less than three years after its 2009 launch.
The second: Snow Leopard users have hung onto the OS. As of the end of February, nearly 28% of all Macs globally were running that edition, slightly more, in fact, than ran its successor, Lion. If Apple stopped serving security updates to Snow Leopard, it would leave a major chunk of its user base unprotected.
Snow Leopard may be Apple's Windows XP, the Microsoft OS that even 12 years after its debut, just won't go away. Like Microsoft, which extended the support life of XP, Apple may be forced to do the same.
When will it pull the plug? That's impossible to say, considering Apple's tight lips.
But Apple supported Snow Leopard's ancestor, OS X 10.5, aka Leopard, or four years. If it patches Snow Leopard that long, Apple will call it quits this summer when it issues the replacement for Mountain Lion.
Or not. At that point Snow Leopard will still power between 22% and 23% of all Macs, based on projections using data from Web metrics company Net Applications.
Security Update 2013-001 is available by selecting "Software Update..." from the Apple menu, or by opening the Mac App Store application and clicking the Update icon at the top right of the screen. The update can also be downloaded manually from Apple's support site.
Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at @gkeizer, on Google+ or subscribe to Gregg's RSS feed . His email address is email@example.com.