I discovered this issue the other day whilst reviewing a design for a client.
The client planned to deploy Exchange 2003 as part of a migration from Novell GroupWise which needed to occur rapidly. There was no time to wait for and test Exchange 2007 in this case. However, it was thought that as Exchange 2007 was imminent, the hardware should be specced accordingly. Therefore, servers were purchased that were 64bit and which had 8GB of RAM.
On reading the design for 8GB of RAM I wondered whether this was a sensible configuration given that Exchange (with the /3GB switch) can only access 3GB of RAM anyway and the box was only going to be running Exchange.
After a little investigation I discovered this article:
Basically, it outlines that having over 4GB of RAM in a box is potentially detrimental to performance as it takes up part of the paged pool just to address the extra RAM which you won’t be using.
So unless you are running multiple roles on one server (not recommended) then you should either remove the RAM phsyically, or use the following switch in boot.ini
/BURNMEMORY=ammount of RAM
So for a server with 8GB
This will mean the OS will not address the extra 4GB in the server.