Mac OS 8.6

Released on 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  8.5.1 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.

Sources and References

 * Mac OS 8