While System 6 was the first Mac OS version I used, I didn’t start really writing Mac apps until the Mac OS 8 era. I was recently having a conversation with another developer who grew up using Macintosh computers and we were both reminiscing about some of our early development experiences on Mac. Finally, after the PowerPC transition, I used a Power Macintosh 8500 which ran all of the later versions of “Classic” Mac OS. Then I moved up to a Macintosh IIsi running System 7. I started using a Mac with System 6 on a Macintosh Classic.
It includes System 1 all the way up to Mac OS 9.x. This is often referred to as “Classic” Mac OS. Before macOS, and before OS X, there was just Mac OS.
