You may have already heard Microsoft’s recent announcement that the next version of Exchange, currently dubbed E12, will ship as a 64-bit application only to run on x64 CPUs. This may have left you wondering what x64 is, how 64-bit technology is going to benefit Exchange, or what you should be looking for when purchasing hardware now, so when E12 ships you are ready.
Today, your typical server contains a 32-bit processor(s) which can use a maximum of 4GB RAM. Windows will split that into two, 2GB chunks, one for kernel mode and one for user mode. You can alter this, and Microsoft recommends you do so with Exchange servers that have more than 1GB ram, by adding the /3GB switch to your boot.ini file. This increases the amount of memory available to user mode applications, such as store.exe, to 3GB, leaving the other 1GB for the kernel. This still limits a 32-bit application to a maximum of 3GB RAM.
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