Co processing and parallel processing.
Co-processing refers to a situations wheretwo central processing Units (CPUs) execute one single program at a go. A program may be run two processors at a single time in a situation wherethe data being processed is complex and bulky.
Parallel processing refers to a situation where a single system handles multiple programs at a time. The CPU attention is switched among the programs on a timed basis controlled the operating system thus it appears as if each program is having uninterrupted access to the CPU.