Edited sentence: A similar "run multiple 7's on a kernel" would simply not work, System 7 was so much larger than System 6 that it barely fit in memory of many 1990-era by itself, the idea of spawning multiple copies for programs would have been impossible.Additionally one key part of the entire Mac OS, QuickDraw, was not able to be used effectively in a protected memory system, for performance reasons it stored state in each application's memory.Although a new version of QuickDraw could have been written, empire building placed all such efforts under the QuickDraw GX project, which was not ready for some time.In 1995 Apple committed itself to providing a microkernel-based system in the Copland project, which staggered on for two years before finally being killed off.Instead System 7 was really an extensive collection of "bells and whistles", dramatically improving the look and feel of the system, but doing little "under the hood".It seems entirely possible that an operating system running multiple independent System 6 "boxes" could have been built that would have run in about the same memory footprint as System 7.It would have also provided the groundwork for a new application model designed specifically for the new OS.Much of the complexity was due to the terribly complex memory management scheme needed to keep the per-application memory footprint within reason, so much complexity that the system was simply never able to stabilize.System 6.0 ran in about 600k, much of which was a set of shared code.Under such a model the operating system would be able to gracefully exit misbehaving programs without causing the system as a whole to crash.With the release of System 7, Apple had perhaps lost a great opportunity to make a truly modern microkernel-based OS