Mac OS 8

Mac OS 8 is a version of the Mac OS that was released on July 26, 1997.

Mac OS 8.0
Main article: Mac OS 8.0

Improvements in Mac OS 8.0 include a multi-threaded Finder, the three-dimensional Platinum appearance theme and a number of performance related improvements to virtual memory, AppleScript execution times and system start-up times. Help was available in the form of an Info Centre (by means of web pages stored on the user's hard drive, with links to the Internet -- this was new with Mac OS 8), as well as Balloon Help and Apple Guide.

Mac OS 8.1
Main article: Mac OS 8.1

Released January 19, 1998, Mac OS 8.1 was the last version to run on Macintosh computers with a Motorola 68000-family processor. It introduced support for the HFS Plus file system format, which supported large file sizes, longer file names and made more efficient use of the space on larger drives due to using a smaller block size. It is the earliest version that can run Carbon apps.

Mac OS 8.5
Main article: Mac OS 8.5

Released October 17, 1998, Mac OS 8.5 was the first version of the Mac OS to run solely on Macintosh computers equipped with a PowerPC processor, as such it removed some but not all of the Motorola 68000 code, improving system performance. It was the first version to include the Sherlock search tool.

Mac OS 8.5.1
Main article: Mac OS 8.51

Mac OS 8.51, released December 7, 1998, was a minor update to Mac OS 8.5 that fixed a number of bugs that were causing crashes and data corruption.

Mac OS 8.6
Main article: Mac OS 8.6

Released May 10, 1999, Mac OS 8.6 introduced the concept of a nanokernel to the Mac OS which allowed for multi-tasking and multi-processors. This free update for Mac users running 8.5 and  8.51 was faster and much more stable than either versions of 8.5.x, and is by some considered the most stable Classic OS. It was also the first Mac OS to have the OS version displayed as part of the MOSS (Mac OS Startup Screen). Many hardware upgrades require a minimum of Mac OS 8.6.