661-3929 512 MB, FB-Dimm, ECC, DDR2 667 - 2-2.66-3GHz Quad - 3GHz 8-Core A1186 Mac Pro NB-2225W This is 512MB DDR2 PC2-5300 RAM upgrade for the Mac Pro. This is for PC2-5300 DDR3 Machines. These are DIMM chips and not SODIMM chips used in MacBooks and iMacs. Apple part number: 661-3929