Sun's X8007A, X8006A, X4211A-Z and Dataram's DRSU20E/1GB, DRSU20E/2GB and DRSU20E/4GB are ECC type memory and should not be mixed with Sun's X8008A Non-ECC type memory. 8GB maximum with ECC memory; 1GB maximum with Non-ECC memory. Dataram's DRSU20E/4GB is PC2700 333MHz; Sun's X4211A-Z is PC2100 266MHz. Other capacities are all PC3200 400MHz.