I do not think that deifnition in britanica of word multiprocessing, as computing termine, is vague. There is a difference from multithreading and multiprocessing I believe. From OS definition, process is an object that encapsulates memory and CPU usage, memory between processes is exclusive. While on the other hand, process can hold a thread or more of them, having threads process shared memory by more cores if possible- multithreading. It is like for me that multithreading promisses a a paralel memory access over more cores in a single process, while multiprocessing promisses parallel processing of processes.So if for example an OS that supports multithreading hold a multiprocessing CPU, it cannot create more than one thread for a process, but can distribute CPUs for those processes that can run parallel smoothly.

This anecdotal information might shed light on things:

I wrote a an application that on Windows Vista ran multi threaded and was clearly using multiple processor cores on an i7 4 core machine. However running the same program on Windows NT and a multi processor, multi core Xeon machine, the same exact executable did not use multiple processors, neither mulitple cores and ran slower than on the single processor machine.

What gives?

spinningcube

Are you sure it was using multiple cores? Windows Vista will do better schedualing that often moves threads between cores, so a single theaded application will use multiple cores, but never two at once.