darrell@sdcsvax.UUCP (02/13/87)
Re: terminology Michael Scott posts: >I find it useful to keep distinct the meanings of the words "concurrent", >"parallel", and "distributed." In the interests of broadening the discussion, >I suggest the following definitions: > > "Concurrent" implies the simultaneous existence of more than one > thread of control. > > "Parallel" implies the simultaneous *execution* of more than one > thread of control. > > "Distributed" implies interaction between threads of control on > processors that share no physical memory. > >Parallel and distributed both imply concurrent. >Most distributed computations are parallel. >Coroutines are concurrent but not parallel. The problem is much worse that this. [Pull out my classic Indian Blindmen describing Nude elephant slide: an elephant is like a wall, no it's like a snake, no, you're both wrong, like a tree...] Other people refer to real-time systems as concurrent systems, also note Concurrent Computer [formerly Perkin-Elmer], and so forth. The Cray and other worlds have problems with: multiprogrammed (easy), multiprocess(or/ing [surprising hard]), multitasking [also surprisingly hard, lots of name collisions here], micro-tasking, et. al. And I set Marty Fouts a little thing about Loosely-coupled versus tightly coupled processing. The use of terminology is not only abomitable, but detrimental. Exercise left to the reader: do some research akin to parallel or whatever computing. Stop using the words "Parallel Process" for a day. Next day remove the obvious synonyms like "Multiprocess," one day at a time: distributed process next, etc. Describe the same concepts. See how much you hand wave. This is akin to the exercise which the guys (correction: humans) studying light did to understand the duelistic nature of light (Light was a particle on MWF, a wave on TTS). Have fun. >From the Rock of Ages Home for Retired Hackers: --eugene miya NASA Ames Research Center eugene@ames-aurora.ARPA "You trust the `reply' command with all those different mailers out there?" "Send mail, avoid follow-ups. If enough, I'll summarize." {hplabs,hao,nike,ihnp4,decwrl,allegra,tektronix,menlo70}!ames!aurora!eugene