Mac OS is a trademark of Apple Computer, but the operating system did not always go by this name. At first, it was called the System. Had no CommandLine of any kind.
The major releases were:
System 6: (especially System 6.0.3, which is the best version of System for your old 68000-based compact Mac). The most recent version of System 6 is 6.0.8.
System 7: This was the first real revolution in Mac OS system architecture, because it added multitasking without having to run MultiFinder (it made MultiFinder a permanent part of the OS and discontinued the "regular" singletasking Finder). System 7.1 Added a number of important features, but had a confusing series of updates that needed to be installed, including "System Update 1", "System Update 2", "System Update 3" and "Hardware System Update 1", and "Hardware System Update 2." This was Apple's way of supporting the unprecedented number of new Macintosh models it was releasing at the time. System 7.1.1 was called System 7 Pro. System 7.1.2 was released on the first Power Macintosh Computers. This introduced the "Type 11" error when any 680x0 code had a bug in it, which the hardware emulator could not resolve. Under a 680x0 machine, this would have caused a Type 1 or Type 2 error, and the application would have crashed, but the computer would still have been usable. Type 11 errors require an immediate halt.
System 7.5 involved no real architecture change, but it added a number of third-party utilities to the OS. It eventually was revised to 7.5.5, but not after having two 7.5.3 releases (7.5.3 and 7.5.3r2). You can download 7.5.3 free from http://download.info.apple.com/Apple_Support_Area/Apple_Software_Updates/English-North_American/Macintosh/System/Older_System/System_7.5_Version_7.5.3/ and the updater to 7.5.5 at http://download.info.apple.com/Apple_Support_Area/Apple_Software_Updates/English-North_American/Macintosh/System/System_7.5.5_Update/
Apple changed the name to Mac OS when it released Mac OS 7.6. This operating system offered a few enhancements. The name was changed because Apple wanted the name Mac to appear on clones of Macintosh computers. Mac OS 7.6.1 was the first operating system to correctly handle 680x0 bugs as Type 1 or Type 2, but it had taken nearly 3.5 years since the release of the first Power Macintosh to achieve a stable OS.
Apple released Mac OS 8 so that it could terminate the license of the cloners, who had purchased licenses to Mac OS 7's incarnations. Apple would not allow cloners to license Mac OS 8. The latest version of 8 is Mac OS 8.6, which is the earliest version of Mac OS that can run carbonized apps.
Mac OS 9 introduced a number of wizzy features. The last version was Mac OS 9.2.2.
No longer in MacOs :(, Clarus the dogcow is now on the net.
The dogcow was an icon on the original Macintosh computer. I don't believe there was a description or name for her and people were unable to determine if she was supposed to be a dog or a cow. She became a sort of mascot for Macintosh users for a while, with amusing stories written about her, etc.
Back in the day, I used TheDogCow as my online handle. -- BrianRobinson