I don't really see any reason to consider process migration a required feature of either a distributed os or a single system image. Even on a single computer th

I don't really see any reason to consider process migration a required feature of either a distributed os or a single system image. Even on a single computer this isn't always practical or desireable (ie. you can't 'migrate' a program running on your gpu to your cpu, and you can't trivially migrate a thread from one process to another either). Not all units of computation are interchangeable, and a system that recognizes this and doesn't try to shoehorn everything down to the lowest common denominator actually gains some expressive power over a uniform system (else we would not have threads).