The DDR2-800Mhz Mac Pro memory is compatible with the 2nd Generation (Early 2008) DDR2-800Mhz. The Mac Pro DDR2 series uses a type of memory called an FB-DIMM. There are four (4) or eight (8) slots, and the FB-DIMMs are installed in pairs (2x at a time). In order to run 256 Bit Addressing modules are installed in two matched pairs (4x identical modules). The original 1GB is installed as a pair of two 512mb FB-DIMMs. The system maximum is 32GB with the installation of eight (8) 4GB FB-DIMMs. Gigaram kits contain a matched set of DIMMs. The kit consists of identical brand/model/spec IC's, with matching batch numbers. Our memory will also mate perfectly with Apple original DIMMs.