Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!shadooby!oxtrap!sendai!rich From: rich@sendai.sendai.ann-arbor.mi.us (K. Richard Magill) Newsgroups: comp.sys.sequent Subject: Re: What? I'm confused. Sequent their strengths & weaknesses Message-ID: Date: 11 Sep 89 17:07:32 GMT References: <17580@bellcore.bellcore.com> <5053@eos.UUCP> <11500@boulder.Colorado.EDU> <83733@pyramid.pyramid.com> <17596@bellcore.bellcore.com> Sender: rich@sendai.UUCP Reply-To: rich@sendai.ann-arbor.mi.us Organization: Digital Works, Ltd. - Ann Arbor, MI Lines: 43 In-reply-to: johno@dduck.ctt.bellcore.com's message of 11 Sep 89 13:06:30 GMT parallel vs multiple. I don't know about the strict definitions but the following are practical differences. Both types of systems have multiple cpu's. The first question to ask is whether any cpu can do i/o or if only a particular cpu can do i/o; (this would clearly be a master/slave system). The second question is rather complex. You want to know whether there is a single run queue, or one per processor and when processes are assigned to processors. A clue to this is how many processors can be in kernel code at one time. Some systems have multiple run queues but only assign processes to processors on fork(2). Others have a single run queue and assign processes to processors at run time. ie, processes can play shell games (like the old 3 card monte) across all of the available processors. Pretty much any other attempt to use the parallelism beyond this requires operating system extensions beyond 4.3bsd and sometimes compiler support. There is currently debate as to whether a compiler "should" produce code that implements parallel algorythms rather than single threaded code. The rudimentary facilities for experimenting on these kinds of algorythms are available on DYNIX. The real (read practical) win of sequent these days is it's robustness. In terms of processing power, it isn't a very deep machine, ie, no single thread runs very fast, but it is a *very* wide machine. That is, you can put large amounts of memory into it, the scheduler is *much* better that the standard bsd or usg schedulers, the disks can be *very* fast so paging is a lower overhead than most machines, and performance degrades very gracefully. Sequent is the kind of machine you want if you need to support hundreds of users at the same time with relatively small amounts of average cpu / user. I should also point out that sequent hardware and software is noted in the industry for it's solidity. That is, very few bugs, and the stuff doesn't break very often. (if you are interested in the down side, let me know. I can flame them into the ground as well as plug them.) xoxorich.