Wondering which versions of macOS your Mac can run? We’ve put together a macOS compatibility checker that will show you what Macs the different versions of macOS and Mac OS X support, so you can tell what version you should be running on your Mac.
What Mac operating systems can my Mac run?
Apple releases a new version of the Mac operating system almost every year—but the new version of the Mac operating system will not support every Mac. Each year more and more Macs fall off the compatibility list and are unable to be updated to take advantage of the latest features.
Read more at Macworld.com