回答“Difference between macOS High Sierra, Yosemite, El Capitan, etc.?”10.4.11 (Tiger) was seriously the best most stable version of Mac OS X ever, but you’re not going to ‘upgrade’ to that now LOL. I still have an old 17” Powerbook G4 that I use as my Print Server for my Apple Laserwriter 4/600 and that one runs Tiger. Most webpages will no longer work with Tiger so that old of an operating system is pretty useless for internet browsing, but I would recommend it if you just needed it for working within applications and not for connecting to the web. For non-subscription versions of classic applications such as Adobe CS, Quickbooks, Acrobat Pro, ol’ Tiger is very capable, rock stable, and fast.