4GB Upgrade for a Apple Mac Pro (4-core Xeon 3500 Series) System (DDR3 PC3-8500, ECC, ) 240-pin DIMM DDR3-1066 DDR3 PC3-8500 Unbuffered, ECC, DDR3-1066, 1.5V, 512Meg x 72 The only brand of memory upgrade available directly from a DRAM manufacturer, tested to meet the most stringent industry specifications Install it yourself in about 15 minutes. The same top-quality memory that the worlds largest computer manufacturers install in the systems they sell