The second major revision supports multitasking, multiprocessing, and message passing, and would be more properly called a microkernel.
[4] Its main purpose is to allow the existing Motorola 68K version of the operating system to run on new hardware.
A forward-looking architecture was introduced for PCI card drivers in anticipation of the Copland microkernel called NuKernel, which supports memory protection.
The DayStar Digital Genesis MP Macintosh clone requires kernel extensions to support multiprocessing.
Mac OS 8.6's nanokernel was rewritten by René A. Vega to add Multiprocessing Services 2.0 support.