How much physical RAM can Exchange 2000 Server make use of?
Windows 2000 gives each process a 4GB virtual address space. Typically, the process gets 2GB of this address space and all system processes share the remaining 2GB. If you use the /3GB switch in boot.ini, processes get 3GB of their address space. Exchange 2000 requires this switch when you have more than 1GB of physical RAM on the Exchange server. Using the switch prevents Exchange 2000 from exhausting its virtual address space, which can happen when unallocated physical RAM remains. You're unlikely to see any performance benefit by having more than 2GB of physical RAM on the server.