I have 16GB of Registered ECC DDR2 RAM in a 4X4GB configuration, but have never come close to using it all. I recently reconfigured my drive arrangement form 8X4TB drives and 2X2TB drives down to 3X2TB drives, involving the need to transfer 3TB of the files off of the server onto an external HDD attached to my computer over a gigabit network connection and the server never used more than 29% of the available RAM