Microsoft recommends not using the /3GB switch on a server running both Exchange and AD if it isn't Small Business 2003 because when you put a /3GB switch into the Boot.ini file of the operating system, you reallocate the virtual address space distribution to give User mode programs 3 GB of space and limit the kernel to 1 GB.
Here's my scenario - We have a one server environment running Windows 2003 Server (Enterprise) and Windows 2003 Exchange (Enterprise) with AD on the same server. The Server is new, a pair of quad core Xeon processors, 16GB of RAM, 15K hard drives. It's a fast box. We only have about 20 users. We use the server as a file server and for Exchange - not much else.
Is there a way to utilize the extra RAM and not shoot myself in the foot? Can we get away with 1GB of RAM for kernet if we allocate the /3GB switch? These users like their large e-mail boxes. Is there a way to tell Windows to keep the 2GB for the Kernel but is X amount for Exchange?