RAM & Memory Upgrades
8GB (2 x 4GB) DDR2 667MHz PC2-5300 240-PIN ECC FULLY BUFFERED (FBDIMM) MEMORY RAM KIT COMPATIBLE WITH MAC PRO (ORIGINAL/2006)
SIZE/CAPACITY: 8GB KIT (2 x 4GB) VOLTAGE/POWER CONSUMPTION: 1.8v CAS LATENCY: CL5 SPEED: PC2-5300 (667MHz) TYPE/INTERFACE: 240-PIN DDR2 ECC FULLY BUFFERED DIMM (FBDIMM) - APPROVED 240-PIN MAC PRO DDR2 ECC FULLY BUFFERED DIMM KIT
https://www.bizrate.co.uk/ram_memoryupgrades/8gb-2-x-4gb-ddr2-oid34741189982.html