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rdalrt

macrumors newbie
Original poster
Feb 15, 2016
12
0
Screen Shot 2021-01-31 at 12.00.29 PM.png
 

Bubu_76

macrumors newbie
Feb 7, 2021
2
0
I would assume that you need to have 3x identical Dimm sizes per CPU - but I am not sure. Didn’t find any precise info how to place RAM with different sizes in a dual CPU Mac for tripple channel. Waiting for my additional memory to arrive this week and will have the same question that you have. Guess we will have to try out with geekbench and see what’s faster. The only thing clear to me is not to use the 4th and 8th DIMM slot.
 

Bubu_76

macrumors newbie
Feb 7, 2021
2
0
The setup described above is triple channel. Same config here. Tested it with the app „CPU-Z“. CPU-z will give u the no of channels used.
 

h9826790

macrumors P6
Apr 3, 2014
16,608
8,532
Hong Kong
Your setup can only works in triple channel. Each slot only connected via one channel. If not in triple channel, then at least one of the DIMM won't work.

However, that doesn't mean you have optimum performance (if that's the "triple channel" you really want to ask).
 

rdalrt

macrumors newbie
Original poster
Feb 15, 2016
12
0
However, that doesn't mean you have optimum performance (if that's the "triple channel" you really want to ask).
Hmm, good point. Is there a recommended app/method for testing memory performance in this config vs six identical 8GB dimms?
 

rdalrt

macrumors newbie
Original poster
Feb 15, 2016
12
0
Just to follow up on this, I had a chance to do some testing in GB3 (64 bit) today.

Test rig:
Mac Pro 4,1 flashed to 5,1.
Intel Xeon E5520 @ 2.26 GHz (memory runs at 1066)
2 processors, 8 cores
Running Mojave

Results: each config. run 3 times, these are the best results from each

Config. #1
48 GB of ram, six identical sticks in slots 1,2,3 & 5,6,7

Memory Performance​


Single-core1778
Multi-core4153

Config. #2
64 GB of ram, 16GB in slots 1 & 5, 8GB sticks in 2,3 & 6,7 (the config. at the top of this thread)

Memory Performance​


Single-core1614
Multi-core2018

Config. #3
24 GB of ram, six identical 4GB sticks in slots 1,2,3 & 5,6,7

Memory Performance​


Single-core1825
Multi-core4282

Config. #4
32 GB of ram, eight identical 4GB sticks filling all slots

Memory Performance​


Single-core1712
Multi-core1967


Not sure what it would all mean in terms of real world performance, but just thought I would post what I found.
 
Last edited:

h9826790

macrumors P6
Apr 3, 2014
16,608
8,532
Hong Kong
It’s easy, despite the multi thread performance is doubled in the optimum memory config. I believe you can’t feel anything. If not using GB, most likely you can’t tell there is any difference.

And this is exactly what it means in real world - almost no difference in most of the time.

In general, just keep it simple. Install as much memory as you can. E.g. you can run 72GB now, then no need to stay at 64GB.
 

poundman

macrumors member
Jul 22, 2011
33
0
I have a similar config with the same processors but running high sierra. I was having trouble installing memory in slot 2. It seems no matter what memory config I can only get single core 445 and multicore around 2900-3000. I am using geekbench 5. I tried 8Gb in slot 1,5 only, then 8gbx6 in slot 1,3,4,5,7,8. I get the exact same scores
 

MrScratchHook

macrumors regular
Dec 17, 2022
216
70
United States
Just to follow up on this, I had a chance to do some testing in GB3 (64 bit) today.

Test rig:
Mac Pro 4,1 flashed to 5,1.
Intel Xeon E5520 @ 2.26 GHz (memory runs at 1066)
2 processors, 8 cores
Running Mojave

Results: each config. run 3 times, these are the best results from each

Config. #1
48 GB of ram, six identical sticks in slots 1,2,3 & 5,6,7

Memory Performance​


Multi-core4153
Single-core1778

Config. #2
64 GB of ram, 16GB in slots 1 & 5, 8GB sticks in 2,3 & 6,7 (the config. at the top of this thread)

Memory Performance​


Multi-core2018
Single-core1614

Config. #3
24 GB of ram, six identical 4GB sticks in slots 1,2,3 & 5,6,7

Memory Performance​


Multi-core4282
Single-core1825

Config. #4
32 GB of ram, eight identical 4GB sticks filling all slots

Memory Performance​


Multi-core1967
Single-core1712


Not sure what it would all mean in terms of real world performance, but just thought I would post what I found.
just max the ram with 8x16, you wont regret it or have any hiccups...
 
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