Comment by flenserboy

It's not 2 mb in particular; honestly, I'd say 4 mb is the practical starting limit once you're into 16/32 bit CPUs — a Mac Plus / Classic would go to 4, for instance, and every speck of memory free under that made a difference in performance. 2 is a nice limit for total system size, as it allows for (as can be seen in QNX) a very capable, flexible OS, while leaving headroom for programs to run.