Product Detail Compatible with Apple Power Mac G5 Dual-Core 2GHz DDR2 Non-ECC (M9590LL/A), Power Mac G5 Dual-Core 2.3GHz DDR2 Non-ECC (M9591LL/A), Power Mac G5 Quad 2.5GHz DDR2 Non-ECC (M9592LL/A). The G5 comes standard with Non-ECC memory unless ECC memory was specially ordered. The maximum memory allowed is 16GB and there are 8 sockets available (4 banks of 2 2pcs 2GB DDR2-533, PC2-4200 DDR2 Non-ECC DIMM Lifetime Warranty and Guaranteed Compatibility . The "Axiom AX - Memory - 4 GB : 2 x 2 GB - DIMM 240-pin - DDR2 - 533 MHz / PC2-4200 - unbuffered - non-ECC" is best product for you. We recommended Axiom AX - Memory - 4 GB : 2 x 2 GB - DIMM 240-pin - DDR2 - 533 MHz / PC2-4200 - unbuffered - non-ECC