What is the meaning of idiosyncratic when refering to multiprocess abstractions?
Let me rephrase your quote:


  Implementations of multiprocessing in various systems tend to be rather different. Each system uses its own peculiar "vocabulary". When we port each such system to new hardware, we need to code afresh the entire multiprocessing subsystem. One way to address this difficulty is to come up with a small set of multiprocessing primitives which, on the one hand, can be used to implement all the multiprocessing mechanisms in known systems, and on the other hand, is simple enough to code for each particular hardware. This will drastically reduce the effort required in porting operating systems.