13.2.1 Parallel Machine Features
RISC architectures are often parallel processing environments. Other parallel processing environments include multiple CPU's (multiprocessing) and multiple ALU's (array processors and supercomputers) and systems with enough back-up components to execute even if there is a hardware error (fault-tolerant computers).
Multiple processors which have their own memory and I/O ports (loosely coupled systems) have different compiler issues from those which have multiple CPU's, but share memory and I/O ports (tightly coupled systems).