12.6. NuBus

Another interesting, but nearly forgotten, interface bus is NuBus. It is found on older Mac computers (those with the M68k family of CPUs).

All of the bus is memory-mapped (like everything with the M68k), and the devices are only geographically addressed. This is good and typical of Apple, as the much older Apple II already had a similar bus layout. What is bad is that it's almost impossible to find documentation on NuBus, due to the close-everything policy Apple has always followed with its Mac computers (and unlike the previous Apple II, whose source code and schematics were available at little cost).

The file drivers/nubus/nubus.c includes almost everything we know about this bus, and it's interesting reading; it shows how much hard reverse engineering developers had to do.