Apple last week released an update for macOS High Sierra, boosting the numeric label to 10.13.5 and simultaneously starting the clock on ending support for 2015's El Capitan.
Approximately one in eight Mac owners currently runs OS X 10.11, otherwise known by the Yosemite landmark of "El Capitan," according to analytics vendor Net Applications. Data published June 1 by the metrics firm said that during May El Capitan powered 12.9% of all Macs.
Apple's update for 2017's High Sierra - the already-mentioned 10.13.5 - patched 32 security vulnerabilities, including critical bugs in the operating system's kernel that were reported by researchers working for Google. The High Sierra update also added support for storing Messages' texts and attachments, such as photographs and videos, in iCloud, freeing up storage space on the Mac's own drive.
Separate security updates, minus the Messages in iCloud feature, were released for High Sierra's two predecessors. Traditionally, Apple supports three consecutive editions of the Mac's operating system: the current and the two previous. If "N" represented the current edition, High Sierra, then Apple was also obliged to offer security updates to "N-1" and "N-2," 2016's Sierra and 2015's El Capitan, respectively.
But a new macOS edition is imminent, which will bump El Capitan off the support list, probably after one more set of security patches.
This week, Apple will unveil High Sierra's follow-up, almost certainly identified as 10.14, at its annual Worldwide Developers Conference (WWDC) in San Jose, Calif. Traditionally, Apple executives have launched the year's macOS upgrade at WWDC, given it a name - another California location is a good bet - touted a handful of its new features or improvements, and parceled out preview copies to developers. There's no reason to think things will be different today, when Apple CEO Tim Cook and other executives take the stage to present the WWDC keynote address.
That address will be live-streamed and begins at 1 p.m. ET/ 10 a.m. PT.
Once macOS 10.14 launches this fall - September will be the most likely, followed by October - it will become "N," with "N-1" and "N-2" standing for High Sierra and Sierra. OS X El Capitan will then drop out of support. At that moment, up to a quarter of all Macs will be running retired operating systems.
That fraction will shrink as users upgrade to macOS 10.14, reducing the shares of High Sierra and Sierra most of all, less so for El Capitan. Over the course of the next 10 to 12 months, the portion of unsupported Macs will gradually decline to around 13%, the percentage that, year after year, continue to rely on outdated software.
Users can expect one more High Sierra security-and-non-security-fixes update before macOS 10.14's debut, at which point the former's future updates will be security-only. For the last two years, Apple has released a single operating system update between WWDC and the launch of the next upgrade. In 2016, that update, OS X 10.11.6, appeared on July 18; the following year, macOS 10.12.6 shipped on July 19. If the Cupertino, Calif. company continues that practice, macOS 10.13.6 will be released July 16-20.
The macOS and OS X updates will be automatically offered on the appropriate devices. Users can manually trigger an update on a Mac by selecting "App Store" from the Apple menu, then choosing "Updates" from the row of icons at the top of the window.