In November, Yosemite accounted for 36.6% of all instances of Apple OS X tallied by Net Applications, which estimates operating system user share by counting visits to the websites operated by its clients.
By comparison, OS X Mavericks, Apple's 2013 upgrade, ended November of that year -- also its first full post-launch month -- with a Mac-only user share of 32%.
Yosemite's pace was the fastest ever for an edition of OS X, beating not only Mavericks but also posting a user share 85% larger than 2012's Mountain Lion and 114% greater than 2011's Lion at their one-month marks.
Yosemite's quicker tempo was in marked contrast to the slower pace of Apple's iOS 8, which continues to lag behind that of last year's iOS 7. Yosemite's adoption also showed that the vocal complaints of still-crippled Wi-Fi have not kept Mac owners from upgrading.
As in October, last month's gains by Yosemite came mostly at the expense of Mavericks, although Mountain Lion and Lion also lost larger-than-average amounts of user share. Mavericks' drop of 13.5 percentage points -- the OS ended November with 38.4% -- was the largest since its launch.
The quicker climb of Yosemite was due to its head start: Unlike Mavericks, Yosemite was offered to Mac owners as a beta, and appeared about a week earlier in its release month.
According to Net Applications, 18% of all Macs ran an unsupported edition of OS X in November. Apple has dropped security support for Lion and earlier versions, meaning that it no longer provides patches for vulnerabilities.
Yosemite's uptake pace was also another validation of Apple's free upgrade policy, which it kicked off in 2013 with Mavericks. According to a Computerworldanalysis of past data from Net Applications, free operating system upgrades accelerate adoption compared to low-priced offers, while low-priced upgrades beat high-cost offers.
Although Apple first acknowledged that five years ago when it slashed the price of OS X upgrades, then again in 2011 before going free in 2013, its OS rival Microsoft has taken longer to embrace the concept.
Microsoft first experimented with a free upgrade last year when it rolled out Windows 8.1, and it will probably extend the practice in 2015 with the launch of Windows 10, which will almost certainly be free to anyone running Windows 8 or Windows 8.1. It's possible that Microsoft will make Windows 10 free to consumers with Windows 7 PCs as well.
The Redmond, Wash. technology giant has also begun giving away Windows to its OEM (original equipment manufacturers) partners that build and sell smartphones, tablets and low-priced notebooks, part of a strategy to compete with Google's Android and Chrome OS operating systems on price points.
The free Yosemite upgrade can be obtained from Apple's Mac App Store, and supports iMacs as old as mid-2007, MacBook Pro notebooks from late 2007 on, and MacBook Air laptops from late 2008 going forward.