The Apple Power Mac G5 Dual can take a maximum of 16GB. When upgrading this system you must install the memory in pairs. Each kit below is 2 modules per kit. ECC memory modules are available for fault tolerant system requirements. APPLE PART# MA246G/A Compatible 1GB DDR2 PC2-4200 DIMM KIT $85.00 APPLE PART# MA249G/A Compatible 1GB DDR2 PC2-4200 ECC DIMM KIT $115.00 APPLE PART# MA247G/A Compatible 2GB DDR2 PC2-4200 DIMM KIT $180.00 APPLE PART# MA250G/A Compatible 2GB DDR2 PC2-4200 ECC DIMM KIT $215.00 APPLE PART# MA248G/A Compatible 4GB DDR2 PC2-4200 DIMM KIT $390.00 APPLE PART# MA251G/A Compatible 4GB DDR2 PC2-4200 ECC DIMM KIT $420.00