We are replacing an existing SQL Server 2005 32-bit environment with a new SQL Server 2005 64-bit Enterprise High availability environment. The new solution will be a 2-node Microsoft Cluster with SQL Server Cluster Server, all 64-bit Enterprise additions. What I have a problem detemining is what is a good baseline for the base memory to install. I will assume that the 64-bit OS & 64-bit SQL will require more memory than the Win2k3 32-bit solution. We will have one instance running initially but we anticipate adding more instances later (probably 2 more). The Dell DL6850 servers have 8 GB but I fear we may need more. Can you suggest a minimum amount of memory to handle the 64-bit OS, APP & 2-3 instances?