If you aren't sure which versions of the Mac OS are compatible with your Macintosh, here are some excellent resources to find out:
AppleCare's Knowledge Base includes several relevant articles on the topic:
- System Software: Version Matrix, System 6.0.x to 7.0.1
- System 7.1 through Mac OS 7.6: Compatibility With Macintosh Computers
- Mac OS 8 and 9 Compatibility with Macintosh Computers
- Mac OS: Versions, builds included with PowerPC Macs (since 1998)
- Mac OS X Versions (builds) included with Intel-based Macs
Now, as for which version of the Mac OS is optimal for your model of Macintosh, well, that's beyond the scope of this article. The folks over at lowendmac.com have a number of helpful articles on this topic, though.