How far back?

[ivnj]

Got new mac mini on August 30th with High Sierra. And trying Mojave beta. Hard drive partitioned in 2. Half HS and half Mojave.

But just out of curiosity how far back does OS support go? I was surprised to see firefox still supports 10.9 since everyone else is on 10.10 at least. Like when Mojave is ready on 24th how long before High Sierra is no longer getting security updates? Or apps stop supporting HS and require update to Mojave?

And after Mojave comes out is El Capitan obsolete? I mean no updates and stuff? How far back does apple go?

 

[baas]

And after Mojave comes out is El Capitan obsolete? I mean no updates and stuff? How far back does apple go?

You're right, the past few years the current release gets x.x.X updates (10.13.1, 10.13.2 etc) and the two latest OS's get security updates so it is expect that when Mojave is released El Capitan lose security updates. Other software vendors usually support the older OS's a bit longer.