OWC 12.0GB (3 x 4GB) PC8500 DDR3 ECC 1066 MHz 240 pin DIMM Memory Upgrade Kit For 2009 Mac Pro and Xserve OWC Memory Upgrade Kit: 12.0 GB (3 x 4 GB) Matched Set PC-8500 1066MHz 240 pin DDR3 ECC SDRAM Modules For Mac Pro Early 2009 & Mid 2010 'Nehalem' & 'Westmere' systems and Early 2009 Xserve, Compatible with PC desktops and PC Servers with Intel / AMD Process based PCs capable with the specifications listed above. Memory complies with JEDEC Specifications, document JESD79-3B Compatible with Mac systems: Mac Pro 8-Core (Mid 2010 Model ID:MacPro5,1 2.4GHz), Mac Pro (Mid 2010 Quad-Core Model ID:MacPro5,1 2.8GHz, 3.2GHz, 3.33GHz), Mac Pro (Early 2009 8-Core Model ID:MacPro4,1 2.26GHz, 2.66GHz, 2.93GHz), Mac Pro (Early 2009 Quad-Core Model ID:MacPro4,1 2.66GHz, 2.93GHz, 3.33GHz), Xserve 8-Core (Early 2009 Model ID:Xserve3,1 2.26GHz, 2.66GHz, 2.93GHz), Xserve Quad-Core (Early 2009 Model ID:Xserve3,1 2.26GHz) High quality, 3 x 4.0GB PC8500 DDR3 ECC 1066MHz 240-pin SDRAM DIMM 512M x 72, Dual Rank ECC Memory Module, 1.5V OWC Lifetime Advance Replacement Warranty Mac Pro 8-Core (Mid 2010)(July, 2010) Model ID: MacPro5,1 (2.4GHz) Mac Pro (Mid 2010 Quad-Core)(July, 2010) Model ID: MacPro5,1 (2.8GHz, 3.2GHz, 3.33GHz) Mac Pro (Early 2009 8-Core)(March, 2009) Model ID: MacPro4,1 (2.26GHz, 2.66GHz, 2.93GHz) Mac Pro (Early 2009 Quad-Core)(March, 2009) Model ID: MacPro4,1 (2.66GHz, 2.93GHz, 3.33GHz) Xserve 8-Core (Early 2009)(April, 2009) Model ID: Xserve3,1 (2.26GHz, 2.66GHz, 2.93GHz) Xserve Quad-Core (Early 2009)(April, 2009) Model ID: Xserve3,1 (2.26GHz) PC Desktops: Compatible with Intel / AMD Process based PCs capable with the specifications listed above PC Servers:Compatible with Intel / AMD Process based servers capable with the specifications listed above <span class="a-text-bold">Size:</span>4GB (4096MB) 240-pin SDRAM DIMM 512M x 72, Dual Rank ECC Memory Module Data Rate = 1066MHz Module Bandwidth 8.5GB/s CAS 7-7-7-20 Voltage 1.5V Apple Specified Thermal Sensor