Of course, Apple can't support its hardware forever. The requirements for compatibility have jumped by a year or so, model-wise, from the Catalina upgrade, with MacBook Air and MacBook Pro models, in particular, jumping from 2012 to 2013. Going further back to 2017, High Sierra ran on many older machines, even going back to 2009. That's moved to largely 2013 models for Big Sur.
Mojave supported Apple computers made from 2012 onwards, while Catalina supported Macs made from 2012 onwards. Catalina and Mojave came after a bit of a cull of support for some older Macs. System requirements for it have jumped a mite over the last couple of years' updates. It's the newest version of macOS, the operating system that powers the Mac and you can read all about it in our macOS Big Sur feature.
(Pocket-lint) - Apple's macOS Big Sur (11) will be available from 12 November.