With Apple poised to introduce its next version of OS X within hours, the current edition, Mavericks, will end its career this fall powering almost three-fourths of all Macs, a validation of Apple's decision last year to give away the operating system.
OS Mavericks increased its share of all versions of Apple's desktop operating system by 2.7 percentage points in May, ending the month on 56.2% of all Macs.
If Mavericks sustains its 90-day average gain through its expected lifetime, it will be on 72% of all Macs by the end of September. Even if Mavericks' growth slows, as it seems to be -- May's increase was sharply off the 4% in April and the 4.2% in March -- Mavericks would still close out September with more than a 70% share of all versions of OS X.
Even Snow Leopard, the previous record holder, didn't reach the 70% milestone before it fell into a long, slow decline after the debut of Lion.
Apple is expected to release OS X 10.10, the successor to Mavericks that may be named "Yosemite," this October. Later today, Apple will certainly trumpet some features of OS X 10.10, may even give it a name and provide a hint of when it will ship.
Like Mavericks, OS X 10.10 will be free to Mac owners, a pledge Apple made last year when it announced it was giving away Mavericks rather than charging the usual $20 for the upgrade.
The move to free, which Apple cast as corporate largess, had baser motives, primarily to bring as many Mac owners as possible to the latest edition so that developers could expect a more homogenous ecosystem, one where most users would be able to take advantage of Mavericks' new features and its latest APIs.
Apple's decision to go free also brought its personal computers in line with its mobile devices, which have long received free operating system upgrades.
The company benefited directly by ditching upgrade fees as well. By consolidating users onto Mavericks, it could reduce support costs. And it could dump the free upgrade programs it had run in the past for those who purchased a Mac between the time of a new edition's announcement and its eventual launch. That program, similar to the one that Microsoft has run for years, carried some incremental costs to administer, required Apple to defer some revenue from the sale of those Macs, and may have made some buyers postpone their purchase until the latest OS was pre-installed.
As Mavericks continued its climb last month, older editions continued to slip into irrelevance. Lion and Mountain Lion ended May with shares of 11.8% and 13.1% of all Macs, while Snow Leopard dropped to 15%.
Even though Snow Leopard has resisted retirement more stubbornly than its siblings, it, too, has accelerated its vanishing act: The three-month average decline of 1.3 percentage points was significantly greater than either the six-month or 12-month averages. At its current pace, Snow Leopard -- dubbed the "Windows XP" of OS X by Computerworld in the past as a nod to its slower slide -- will dip under the 10% mark in November.
Net Applications calculates operating system user share with data obtained from more than 160 million unique visitors who browse 40,000 Web sites that the company monitors for clients.
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 firstname.lastname@example.org.