Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!apple!goofy.apple.com!esmith From: esmith@goofy.apple.com (Eric Smith) Newsgroups: comp.unix.aux Subject: Re: 4 Megg SIMMs. Should I or shouldn't I? Message-ID: Date: 7 Nov 90 23:20:16 GMT References: <121667@tiger.oxy.edu> <18741.2734aee5@windy.dsir.govt.nz> <1990Nov6.041551.2038@panix.uucp> Sender: usenet@Apple.COM Organization: Frobozz Magic Widget Company Lines: 22 In-reply-to: alexis@panix.uucp's message of 6 Nov 90 04:15:51 GMT In article <1990Nov6.041551.2038@panix.uucp> alexis@panix.uucp (Alexis Rosen) writes: > In any event, you probably don't want to do this. The money you spend on the > board could instead go to 4MB SIMMs. Furthermore, access to that RAM would go > over NuBus, and would thus be _slow_ compared to regular memory. (I seem to > recall a minimun 300ns access time, though I'm not sure. That would make it > about 4 times slower, although you might make some of it back on wait states > you wouldn't need.) 300 nS is the minimum CYCLE time. On a Macintosh IIx, the RAM on the logic board is run with 255.3 nS cycles, which is not that much faster than the maximum NuBus speed. Then again, there is a synchronization delay to access NuBus, and many (most?) NuBus cards don't run a maximum theoretical speed. I don't know exactly how fast the Macintosh IIfx runs DRAM cycles, but it can't be much faster than 200 nS (most 80 nS RAMs are spec'd for about 190 nS cycles). I would expect that main RAM access on the IIfx would be about twice the speed of a fast NuBus card. -- Eric L. Smith Opinions expressed herein do not necessarily reflect those esmith@apple.com of my employer, friends, family, computer, or even me! :-)