Xref: utzoo misc.forsale:7138 comp.sys.mac:36202 Path: utzoo!censor!geac!jtsv16!uunet!tut.cis.ohio-state.edu!mailrus!ncar!husc6!think!mintaka!jtw From: jtw@lcs.mit.edu (John Wroclawski) Newsgroups: misc.forsale,comp.sys.mac Subject: Re: SIMM speed rating (was Re: 256K SIMMS forsale!) Message-ID:Date: 9 Aug 89 17:23:54 GMT References: <460@mit-amt.MEDIA.MIT.EDU> <24441@iuvax.cs.indiana.edu> Distribution: usa Organization: MIT Home for Wayward Triumphs Lines: 29 In-reply-to: truel@iuvax.cs.indiana.edu's message of 9 Aug 89 16:12:00 GMT In article <24441@iuvax.cs.indiana.edu> truel@iuvax.cs.indiana.edu (Bob Truel) writes: In article <460@mit-amt.MEDIA.MIT.EDU> adam@mit-amt.MEDIA.MIT.EDU (Adam Glass) writes: >You're quite wrong. Mac II series computers will work just fine with 150ns >SIMM chips. For all normal use, there is no apparent slow down at... I don't know about these new dynamic memory, but it used to be that speed rating had nothing to do with how fast the chip did anything. Um, sorry to disagree, but. The speed rating (access time) of a memory chip is the guaranteed maximum time between when when you set the inputs (address, etc) and when the data appears on the output lines. (Actually, a chip will have different access times for the different inputs - row address strobe, column address strobe, and chip enable...) Chips with faster access times make the data available faster. However, as you point out, this doesn't speed up a Mac II, which cares only that the data be available in 120ns. The reason that a 150ns SIMM generally works in a Mac II is that the 150ns is a worst-case time, assured over the chip's entire permissible range of temperature, power supply voltage, etc. Under normal conditions an average "150ns" SIMM will produce the data much faster than that, and things will work fine. However, if the SIMM actually ever does take the full 150ns, you will lose. Since this will only happen some of the time, you will probably lose in a particularly confusing manner. -john jtw@lcs.mit.edu