4GB DDR3 ECC 1066MHz SDRAM for Early 2009 to Mid 2010 Mac Pro Models 4.1 and 5.1 quad-core and 8-core. Contains one (2) 4GB ECC SDRAM memory modules that are specifically designed and SPD configured for the Nehelam and Westmere Mac Pro Models (3rd Generation). This ECC DIMM includes the Apple Specified Thermal EPROM Sensor that is compatible with the latest Apple firmware Specifications: Total Capacity: 4GB Bus Speed: DDR3-1066MHz (PC3-8500) Form Factor: ECC DIMM, Dual Rank, Unbuffered No. of Pins: 240 Voltage: 1.5V CAS Latency: 7-7-7-20 Cycle Time: 5ns Bandwidth: 8.5GB/s ROHS Certified