I have probably commented this before, but the nommu support was merged all the way back in 2.5.46, so a mmu is certainly not a requirement for running Linux.

I have probably commented this before, but the nommu support was merged all the way back in 2.5.46, so a mmu is certainly not a requirement for running Linux. A 32-bit architecture is not really a requirement either, you just need a compiler that can be told to use 32-integer types and pointers. You probably also have to modify the compiler to generate accesses to your external ram for loads and stores. The real thing preventing you from running Linux on 8-bit micros is the requirement of a von Neumann architecture (or something that looks like it). These small MCUs usually don't even have a way of loading code at runtime which makes it impossible to run any sort multitasking without interpretation.