OWC 128GB (8 X 16GB) PC10600 DDR3 ECC-Registered 1333MHz 240 Pin Memory Upgrade Compatible with Select 2009-2012 Mac Pro Models Model ID: MacPro4,1 MacPro5,1 ; Total capacity - 128GB ; kit module - 8 x 16GB modules ; data rate - 1333MT/s ; ECCR ; form factor - DIMM ; DDR3 ; pc speed - 10600 ; 240-pin ; Fully compliant with JEDEC specifications; OS X versions prior to 10.9 Mavericks are unable to utilize more then 96GB RAM due to an operating system limitation. 128GB can be fully utilized by a 2009-2012 Mac Pro if running OS X 10.9 Mavericks or later, or if running Bootcamp with 64-bit versions of Windows XP and later, as well as with 64-bit versions of Linux. OWC p/n OWC1333D3MPE4GB (4GB modules), OWC1333D3MPE8GB (8GB modules) and OWC1333D3MPE16G (16GB modules) require that all installed modules be of the same p/n OWC4GB, 8GB and/or 16GB modules. Other existing Apple or 3rd party 1GB, 2GB and 4GB modules are not supported for use with these kits and need to be removed when these modules are added. To utilize over 32GB of memory in your Mac Pro using 10.6.x or greater, you must boot into 64 bit mode. In 32 bit mode, all installed memory will show in system profiler but only up to 32GB will be actively used by the computer.