RAM for G5 tower

jmph

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Hey all,
I have a very late Mac G5 2.3dc tower (PCIe based) that I'm putting back into service.
Right now it has two 2GB PC2-4200 unbuffered ECC memory modules that it is recognizing as only 1GB each. The rest of the RAM sticks (2x1GB, 2x512MB, 2x256MB) are reported correctly. Internet wisdom seems to say this model supports 2GB DIMMs

The only thing I can figure is these are double-sided DIMMs (chips on both sides) - maybe it only sees a single side?

Any ideas on how to get it to see the full capacity of the RAM?
 

BLTCON0

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Not familiar with Macs but I have a feeling it has to do with whether the DIMM is single or dual bank (this has nothing to do with single or double sided).
Probably this Mac with its 8 DIMM slots and 2 banks per slot expects 1 GB per bank maximum.
Your DIMMs have 16 chips (I will ignore ECC which doesn't matter here) - now if they use x8 chips all is good, because 8 x8 chips complete a bank so 16 of them are two banks, so 1 GB per bank.
But if the chips are x4 type, then all 16 are required to complete a bank, so despite the double-sided appearance each DIMM squeezes 2 GB in a single bank which the Mac probably can't handle.
So you'll have to get the datasheet for the chips used on the modules and see if they're x4 or x8 type.
 

BlindGerMan

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No Problem to mix 1 GB and 2 GB ddr2 simms in a late G5. They must all be ddr2-4200 and best are Kingston rams!
ATTENTION: Please do NOT mix ecc and non ecc ram! This may damage your board!!!!
 

jmph

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Problem "solved" (actually never existed, see below)

Not familiar with Macs but I have a feeling it has to do with whether the DIMM is single or dual bank (this has nothing to do with single or double sided).
Probably this Mac with its 8 DIMM slots and 2 banks per slot expects 1 GB per bank maximum.
Your DIMMs have 16 chips (I will ignore ECC which doesn't matter here) - now if they use x8 chips all is good, because 8 x8 chips complete a bank so 16 of them are two banks, so 1 GB per bank.
But if the chips are x4 type, then all 16 are required to complete a bank, so despite the double-sided appearance each DIMM squeezes 2 GB in a single bank which the Mac probably can't handle.
So you'll have to get the datasheet for the chips used on the modules and see if they're x4 or x8 type.

Thanks for the VERY consise and useful description of what single bank / dual bank means - I'd seen this term thrown around on Apple forums without any clear explanation of what it meant. I thought it referred to single/dual sided or number (9/18 ) of chips.

ANYWAY... Turns out my memory is specifically intended for G5s and is working fine. The problem is that Kingston's part number G5533E/2G refers to a 2G kit of 2 DIMMs with 1GB per physical DIMM. I've never seen RAM marketed so stupidly. So I really have two 1GB modules and they are doing what they're supposed to. Crisis averted, sheesh, but man I feel like a dope.

- - - Updated - - -

No Problem to mix 1 GB and 2 GB ddr2 simms in a late G5. They must all be ddr2-4200 and best are Kingston rams!
ATTENTION: Please do NOT mix ecc and non ecc ram! This may damage your board!!!!

This isn't true at all, Apple's user manual even states you can mix ECC and non-ECC in the same system. This board takes RAM in matched pairs and as long as you don't mix parity within a pair it will be fine. The DIMMs in same-numbered slots of the upper and lower banks must match. Please don't post incorrect info without fact-checking for accuracy first.

My problem wasn't related to mixing sizes, it was due to me misreading the memory specs from the part number as stated above. All's well now.
 
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BLTCON0

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@jmph
You're welcome. Indeed this 'kit' nomenclature can cause some misunderstandings!

As for mixing ECC and non-ECC, although the way BlindGerMan worded it is indeed incorrect, I'm sure he was referring to mixing registered vs non-registered modules (as the overwhelming majority of ECC-capable modules are registered anyway, being server-oriented since ECC seems to generally be considered unimportant for all but the very high-end workstations, upper-class Macs included). Reg vs non-reg mixing can indeed result to damage and there isn't a single case I've seen it as supported. In fact the only case I can somehow see it working is in NUMA setups, with a separate memory bus to each memory node and some electrically independent node interconnect, and that's assuming each memory controller can take either reg or non-reg RAM AND the BIOS allows that.

Most systems can take only one type anyway and clearly state which one. Some can take either. An example is the new Mac Pro, but of course it can't take both at the same time (and it exclusively requires ECC either way, cool).
 
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