This Machine can take ECC or non-ECC memory. When you mix ECC with non-ECC, the ECC function will be disabled. For the non-ECC memory see "Hewlett Packard Vectra VL800 P4/1.4G (non-ECC) Memory". This Machine may require a BIOS upgrade to use 8 device 256MB, 4 device 128MB, or 2 device 64MB Rambus modules.