OWC 64GB (4 x 16GB) PC10600 DDR3 ECC-R 1333MHz DIMMs Memory Compatible with Mac Pro Early 2009 & Late 2010 'Nehalem' & 'Westmere' Systems and Early 2009 Xserve. (OWC85MP3S9M064K) at Amazon.com
Amazon.com: OWC 64.0GB (4 x 16GB) PC3-14900 1866MHz DDR3 ECC-R SDRAM Memory Upgrade Kit, ECC Registered Compatible with Mac Pro 2013 (OWC1866D3R9M64) : Everything Else
64GB (4x 16GB) Memory for Apple Mac Pro Mid 2010 5,1 12 Core DDR3 1333 ECC RDIMM | eBay
Amazon.com: OWC 64GB (2X 32GB) PC3-10600 1333MHz DDR3 ECC-R SDRAM Memory Compatible with Late 2013 Mac Pro (OWC1333D3Z3M064) : Everything Else
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64GB (4x16GB) DDR3-1600MHz PC3-12800 ECC RDIMM 2Rx4 1.5V Registered Server Memory by NEMIX RAM at Amazon.com
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Kingston Technology Value RAM 64GB Kit 1600MHz DDR3 ECC CL11 DIMM DR x 4 with TS Intel Desktop Memory at Amazon.com