You'll need to know the exact kind of Mac you're using before proceeding-typing your serial number into this Service and Support page should give you the information you need if you're not sure. None really tell anyone in that 19 percent what to do next. Some make a bigger deal about it than others. Most compare the OS X support cycle to the much longer Windows cycle. All point out the same Net Applications data that says 10.6 still powers around 19 percent of Macs.
This has prompted a flurry of posts from various outlets. It's the first major security update that Snow Leopard has missed-the OS is still getting iTunes updates, but its last major security patch happened back in September. When OS X 10.9.2 was released earlier this week, it was accompanied by security updates for OS X 10.8 and 10.7 but not for 2009's OS X 10.6. Since switching to a yearly release cadence with Lion back in 2011, Apple seems to be willing to support whatever the latest version is, plus the two preceding versions. The best you can do is look at historical data.
Apple offers no end-of-life roadmaps for its operating systems, and it doesn't officially comment on whether support has dried up for this or that version of OS X.
