I'm running Sierra on a Mac Pro 5,1. I've got 48GB (6x 8GB) of RAM and after updating to the last security update I've got a RAM conflict, I've swapped some modules position and I could get just 32GB working.

I've already faced that when I upgraded to Yosemite before switching to Sierra, but never with security updates.

Any idea on what’s causing that? It seems the Mac OS X doesn’t allow modules from different batches, quite weird that behavior.

  • It certainly allows modules from different batches. I have a 3,1 with 26GB - 2x8, 2x4, 2x1. Are the slots correct? - support.apple.com/HT205043#1 – Tetsujin Nov 15 '18 at 19:14

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