For Mac OS X, the ideal would be to eventually use the native GUI. (damned inconvenient). I run DOSBox sourceforge.net, which emulates not just the CPU, but the sound card and video adapter as well! The overhead is horrendous (Sword of the Samurai takes more than half the cycles on my 1 Ghz Pentium III), but well within the capacity of my. Choose About This Mac in the Apple menu; and in the window that appears, look beneath 'OS X' to see the version number. Mountain Lion is 10.8. X; Lion is 10.7. The two previous systems are. The maximum version of Mac OS X, OS X, or macOS supported by each G3 and later Mac follows. For complete specs on a particular system, click the name of the Mac. For all Macs that are compatible with a specifc maximum supported version of Mac OS X - courtesy of EveryMac.com's Ultimate Mac Sort - click the OS of interest.
Or use Startup Manager as your Mac starts up: