128GB in a 12-core Mac Pro is recognized and used. Note also that there is better info about how it is used (File Cache, Compressed, App Memory, Wired Memory).
OWC has confirmed what follows: Mavericks properly supports 128GB in a 12-core 2010 Mac Pro.
Bad news on the 4/6-core from OWC:
Nope, still no go, can't even get the OS to load with 64GB in my 6-core.
Apparently a hardware limitation with the 4/6 core model processor tray/chipset
Those who actually need 128GB of memory for about $1460 now have a reason to (a) upgrade to OS X 10.9 later this year, and (b) can save a ton of money over having to buy four 32GB modules for a new Mac Pro. How about a current model 12-core 3.46 GHz stuffed with 128GB and 4 X 4TB internal drives and ~2TB of internal PCIe SSD? You’ll have to live with 96GB in the short run, but that’s maybe not so bad.
Load up your Mac Pro ?
- A 4/6-core 2009 or 2010 Mac Pro will be able to go use 64GB as 4 X 16GB instead of the 48GB limit in OS X 10.8 Mountain Lion (to be confirmed).
- A 12-core 2010 Mac Pro will be able to go to 128GB as 8 X 16GB instead of the 96GB limit in OS X 10.8 Mountain Lion. 8-core models likely to see similar capability.
Image below is of an 8GB module (just more interesting visually, the 16GB module has heat sinks that hide the details).