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macrumors newbie
Original poster
May 28, 2019
Dear friends, I have a base model Mac Pro 2013 (trashcan). I have upgraded its memory to 32 GB, so right now I have two memory modules installed, 16 GB each (1866 MHz)

My problem is: I have ordered 2 extra memory modules (each 32 GB) from OWC. And I am not sure if I can use all of them together, because according to official documentation Mac Pro 2013 only supports up to 64 GB RAM.

Does any of you have any idea if it is supported to combine these modules and have 96 GB in total? Or do I have to remove existing 2 16 GB modules to utilize 2 32 GB new modules?


macrumors regular
Aug 2, 2014
This should work. Right now I have 80 GB in one of my trashcans (2x32 and 1x16). It will take 128 GB max.


macrumors P6
Feb 8, 2003
The Peninsula
Lower, 1066Mhz. There is a speed hit yes.
There is a frequency hit, yes. Often that does not translate into a performance hit for applications.

The big on-chip caches hide lots of memory latencies, and the additional RAM will help apps run faster if you are under memory pressure - and will be filesystem caches to eliminate some IO if you aren't under memory pressure.

Geekbench or other artificial memory benchmarks may show slightly lower performance with slightly slower memory - but most likely in real world performance more memory will be faster.

One of my servers with 2133 MHz memory DIMMs is running them downclocked to 1600 MHz because of the number of DIMMs installed. No way that I would cripple the system by removing DIMMs to get the clock speed up.


(Yes, 2 TiB of RAM.)


macrumors newbie
Original poster
May 28, 2019
Thanks everyone, it worked well. By the way I have learned that Vmware Fusion has a limit of 64 GB per VM. It was a surprise for me :/


Nov 5, 2010
Just a side thought if you are using this for VM's and need a VM with support for more than 64GB RAM, the trashcan can run ESXi - i.e. just turn it into a hypervisor and just run VMs off it. ESXi on it's own is free. Failing that use Linux, you can have a mixture of VMs and containers.
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