From: [EMAIL PROTECTED] Date: Thu, 9 Oct 2003 19:05:59 EDT Subject: Re: 128mb simms for Nubus (was "Joystick")
After the reading the fine print I discovered this is a "kit" of four (4) 64 MB
RAM modules -- not the one module I expected. Sorry, my mistake.
More searching revealed a true 256 MB RAM module.
NOTE: the product description states "This memory was designed for the Apple Power Macintosh PowerMac 6100/60, 6100/60av, 6100/66, 6100/66av."
Well that is interesting and implies either a 13th address line, or that the memory controller/ROM in the 6100 can handle more banks per SIMM, which means splitting up the CAS lines I think.
I would dearly like to know how that one company knew to build a 256 MB module specifically for the 6100. What do they know that we don't and how did they find out? Can you email them?
Anyone know how banks are created on a SIMM?
Unless there is some affordable way of attaining the 520 MB RAM upgrade I will be happy to stay with the 264 MB I have in my 6100's. It provides all the RAM I actually need.
Well, you could always go back to the SIMM Doubler idea. A google search on SIMMverter (one brand) turns up many hits that might be helpful. I did not follow them up. Also, you might check under computer memory on Ebay, but not in the Apple section--in the general PC section. A final possibility is to post a WTB (want to buy) in rec.forsale.computers.memory.
Really want to thank you for your time and the information provided --glen (digest mode)
You're very welcome. (also in digest mode)
This does bring up the interesting question of why the 7100 and 8100 don't appear able to handle the larger SIMMs. Has anyone dug into the reasons for that? They use the same memory controller chip and the 7100 has the exact same ROM. The 8100 ROM is only slightly different.
The facts, as I understand them (could be wrong somewhere), lead me to believe that the 6100 SIMM sockets are actually wired differently, with either additional address lines or more of whatever allows multiple banks (CAS lines?). That would seem to contradict the Apple documentation though. They should all have 12 address lines.
If the 7100 or 8100 had fewer than 12 address lines then the documentation would not just be incomplete, it would be flat out wrong. Twelve address lines should be enough to support 128 MB SIMMs. Perhaps thirteen are needed (e.g. 12/12 isn't support, only 13/11 or 11/13) and only the 6100 has the thirteen address lines.
I guess it's also possible that the ROM has a branch in it that says, "if we're in a 6100 support more RAM modes." But if that were the case, then adding the NuBus adapter to the PDS slot (about the only way the 6100 has of telling it is not a 7100) would make some RAM not work, I think. Unless there's a bank of resistors that support an ID code.
But this latter hypothesis raises bizarre questions about the mind set of Apple engineers who would insert unsupported memory modes into the 6100 and go to a lot of trouble to disable them in the 7100 and 8100. It doesn't seem like the type of engineer who would add undocumented features would then take them away in two of the three models. So I strongly doubt the branching ROM hypothesis.
Very strange. A few experiments suggest themselves, starting with mapping the connections between the SIMM socket and the HMC chip with an ohmmeter. Also, changing the ID on a 6100 board to make it look like a 7100 (however that's done) and see if memory support changes.
One of these days. I should make a "one of these days" list and use it as my sig line....
Jeff Walther
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