Path: utzoo!attcan!telly!lethe!torsqnt!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!wuarchive!uunet!visix!amanda From: amanda@visix.com (Amanda Walker) Newsgroups: comp.sys.mac.hardware Subject: Re: Memory speeds can be critical (was: SIMMs for IIsi - what do I need?) Message-ID: Date: 21 Dec 90 19:28:21 GMT References: <2924@ux.acs.umn.edu> <2946@ux.acs.umn.edu> Organization: Visix Software Inc., Reston, VA Lines: 43 In article <2946@ux.acs.umn.edu> dhoyt@vx.acs.umn.edu writes: >It's a matter of how much difference in speed (and other electrical) >differences the memory drivers can handle. Can you give a detailed example of these differences? I still can't come up with any relevant differences that come into play only in combinations of dissimilar SIMMs. I mean, if we were talking about asynchronous memory subsystems, you might have a good point. However, we're talking quite vanilla dynamic RAM subsystems, which in my experience just don't act in the ways you seem to be claiming they do. This experience includes designing and building DRAM subsystems, as well as actually using mixed-speed SIMM banks in a Mac II without any mishap whatsoever. >Variation between banks is then >adjusted so the entire memory subsystem looks to be the same. "Adjusted?" What do you mean? The Mac memory circuitry, and any other conventional DRAM support logic, does not and cannot do any dynamic adaptation to the speed of the memory, since, as I have said before, It has no way to tell what that speed is. DRAM signal sequencing does not involve any feedback from the memory itself. Even memory support logic that has been designed to handle different speeds of memory has to be explicitly configured (via jumpers or something similar) for the appropriate speed. >In the micro market place the best case might be undefined (because nobody >knows to ask) but the real world the best case is designated as well. Since the IIsi is part of the micro marketplace, and was designed to use mass market memory, Cray memory design contraints are pretty irrelevant, wouldn't you say? Look, as I said before, I'm not trying to argue with reality, it's just that this "same-speed" claim contradicts both my own experience and my understanding of dynamic RAM technology, which so far has served me in very good stead... -- Amanda Walker amanda@visix.com Visix Software Inc. ...!uunet!visix!amanda -- "Furious activity is no substitute for understanding." --H. H. Williams