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flaubert

macrumors 6502
Original poster
Jun 16, 2015
469
184
Portland, Oregon
Hi, I recently scored a 12 core Mac Pro 5,1 to replace my current 6 core model (I love company auctions, especially when the IT department can't be bothered to test equipment, and thus sell perfectly good computers as scrap :cool: ).

My old 6 core 5,1 has four 8GB ECC ram modules, completely filling the four slots available in the six core memory bank. I'm wondering... would I see a big performance hit if I just split the four modules into groups of two, and put a pair of 8GB modules in the memory bank for each processor of the 12 core model? I seem to recall that three modules is ideal, four a little less so, but I can't recall anyone talking about only two memory modules in a bank.

I also have some 4GB and 2GB memory modules. I could, for instance, put three or four of one size in one memory bank, and three or four of another size in another memory bank; is this OK to do?

Finally, what is the advisability of mixing different memory module sizes in a given bank? Could I put two 8GB modules and two 4GB modules in each processor's memory bank, for a total of 48GB? Are there special RAM parameters that have to match for this to be OK?

Thanks for your advice.
 

ifrit05

macrumors 6502a
Dec 23, 2013
547
382
Near Detroit, MI. USA
It's usually not a good decision performance wise to mix modules in a given bank. I have not tried it but not even sure the Mac would like that, might spit out memory errors on boot.

You could mix modules in different banks, just match them in their other corresponding banks, though the speed will drop down to 800/1066 or something like that. Again, not really sure.

I have all slots filled with 8GB of 1333 MHz memory. It runs fine and reports as 64GB@1333Mhz, 1333 being the max Westmere is capable of doing but it will drop it down to dual-channel. You trade a little speed for quantity. It all just depends on your workload requirements.
 
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tsialex

Contributor
Jun 13, 2016
13,117
13,315
Buy two more identical modules and then install six identical DIMMs to your dual CPU tray. Use the smaller modules with your original Mac Pro.
 
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