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Max RAM in 2009/12 Single Core is actually 56GB w/"W" Xeon and 64GB w/"X"
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I have tried this with 3 Samsung 16GB sticks and one 8GB Nanya stick. It boots and runs fine, but bumps the ram down to 800MHz.
Are you getting any ram red lights? Do you absolutely need that 8GB?
Thats because of the Mac Pro's triple channel ram configuration, and that you're using a different capacity than the others slots for the 4th slot. You're probably better off with just 48GB and keep the full bandwidth utilized, as 666sheep already mentioned years ago:
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Haha aren't we all? Well I wish I could be curious just once, but i'm always curious.
I was using 3 of these: https://eshop.macsales.com/item/Other World Computing/1333D3MPE16G/
and 1 of these: https://eshop.macsales.com/item/Other World Computing/1333D3ECC8GB/
Looks like the 16Gb ones are not compatible with the 8Gb ones in this case.
I wanted to test how much of a performance hit the single channel mode would mean in a real world scenario, as I work with large sample libraries I really need those extra 8Gb.
Looks like I will stick to 48Gb for now...
It's nothing to do with 8G or 16G, it's UDIMM vs RDIMM. You simply can't mix them together.
OWC know it, but they didn't clearly state the fact. However, they have the following "note"
IMPORTANT OWC NOTE:
OWC p/n OWC1333D3MPE8GB (8GB modules) and OWC1333D3MPE16G (16GB modules) require that all installed modules be of the same p/n OWC 8GB and/or 16GB modules. Other existing Apple or 3rd party 1GB, 2GB and 4GB modules are not supported for use with these kits and need to be removed when these modules are added.
Since your 8G stick is not the same part number as the above mentioned. That's why it won't work.
For me, it means:
1) OWC know RDIMM cannot mix with UDIMM, and Apple stock RAM is UDIMM, therefore, they have this "notes" to tell the customer that their RAM (which most likely are RDIMM) can't work with the stock RAM.
2) Your 8G stick is UDIMM, therefore, there is no notes on that page, and you can use that stick with the Apple stock RAM.
3) Your 8G UDIMM stick cannot work with the 16G RDIMM stick, which also fit the OWC note.
Anyway, the penalty in real world should be negligible for most of the work, especially you really need the RAM. Running out of RAM always has higher penalty than not optimising the triple channel configuration.
OWC know it, but they didn't clearly state the fact. However, they have the following "note"
IMPORTANT OWC NOTE:
OWC p/n OWC1333D3MPE8GB (8GB modules) and OWC1333D3MPE16G (16GB modules) require that all installed modules be of the same p/n OWC 8GB and/or 16GB modules. Other existing Apple or 3rd party 1GB, 2GB and 4GB modules are not supported for use with these kits and need to be removed when these modules are added.
Since your 8G stick is not the same part number as the above mentioned. That's why it won't work.
For me, it means:
1) OWC know RDIMM cannot mix with UDIMM, and Apple stock RAM is UDIMM, therefore, they have this "notes" to tell the customer that their RAM (which most likely are RDIMM) can't work with the stock RAM.
2) Your 8G stick is UDIMM, therefore, there is no notes on that page, and you can use that stick with the Apple stock RAM.
3) Your 8G UDIMM stick cannot work with the 16G RDIMM stick, which also fit the OWC note.
Anyway, the penalty in real world should be negligible for most of the work, especially you really need the RAM. Running out of RAM always has higher penalty than not optimising the triple channel configuration.
That's what I suspected. Would replacing the 8Gb stick with a RDIMM work do you think? Or is it better to go with UDIMM for all of them?
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Get a single 8G RDIMM ECC stick is much much easier and cheaper than get 3x 16G UDIMM ECC sticks.
I installed an additional 8 Gb ram RDIMM stick today and it worked perfectly. There doesn't seem to be any drop in memory performance at all according to Geekbench. All four sticks are running at 1333 MHz.
I can highly recommend this upgrade for anyone who wants to max out the ram to 56Gb in a 2009/2012 single core.
I can highly recommend this upgrade for anyone who wants to max out the ram to 56Gb in a 2009/2012 single core.