From: jsm1@crux1.cit.cornell.edu (Jason S. MacDonald)
Subject: Re: LC Ram Upgrade will be SLOW!
Nntp-Posting-Host: crux1.cit.cornell.edu
Reply-To: jsm1@cornell.edu
Organization: Ono-Sendai Corporation
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douce@tfsquad.mn.org (Andrew Geweke) writes:
>        I cannot speak for Dale. But I am quite sure that the Macintosh 
>uses the full 16-bit or 32-bit data path to its full advantage. That is, 
>it is running as fast with two or four 30-pin SIMMs as it would with one 
>72-pin SIMM. Now, it may be that longword accesses (assuming a 32-bit 
>data path here) get the first byte from the first SIMM, the second byte 
>from the second, and so on. This would mean that each longword of memory 
>is actually split among four SIMMs, one for each byte. On the other hand, 
>it could be that the SIMMs are interleaved by word or longword (not just 
>by byte), or they could be successive in memory, and the memory 
>controller deals with the eight-bit data path that each one has. I 
>suspect, though, that they are interleaved to some extent so that 32 bits 
>can be read or written at once. This would indicate a byte-level 
>interleave.
>        I am NOT confusing this with the new machines' longword 
>interleave with two 72-pin SIMMs of the same sort, although that seems to 
>be the same sort of idea. There, you get an essential 64-bit data path ro 
>(excuse me, to) RAM instead of just a 32-bit one. Yes, the CPU can't 
>handle it, but when writing to successive addresses it speeds something 
>up.
>        So, Dale, am I right? 30-pin SIMMs are interleaved by bytes, 
>allowing the full data bus? Or, as is common with Usenet and me in 
>particular, am I as clueless as everyone else?

What conclusion can be drawn from this?  I'm trying to figure out what kind
of memory configuration for the LC III (32-bit datapath) would be fastest.  Any
ideas?

Thanks,
Jason MacDonald
--
- Jason Scott MacDonald -      jsm1@cornell.edu - jsm1@crux3.cit.cornell.edu
"Technology sufficiently advanced is        ____
 indistinguishable from magic."             \  /      "Cats exist so that we
                 -- Arthur C. Clarke         \/        may caress the lion."
