Crucial 8GB Kit (4GBx2) DDR2-800MHz (PC2-6400) CL5 ECC FBDIMM w/Apple Heat-spreader - CT2KIT51272AP80E / CT2CP51272AP80E Apple Mac Pro 8-core Xeon 5400 Series An FBDIMM will not fit into a standard DDR2 socket, and a DDR2 module will not fit into an FBDIMM socket.