Recently I have been doing some design work for an Exchange 2007 deployment and needed to establish the C drive size for the servers. To do this I realised that the paging file must be accommodated. With x86 (32 bit) Windows Server OSs this is not a big problem becasue 32 bit servers can only address 4GB or virtual memory. On top of this, in general 32 bit servers tend to have 4GB or less RAM installed.
This means that to follow MS guidelines and have a page file of 1.5 times the amount of RAM installed (or 1 times + 10Mb depending on what you read), you still don’t need a massive C drive (12GB would do).
So what happens when you translate this to an x64 server with possibly 16GB or more RAM. Well the C drive just gets a lot bigger. The rule still applies as stated above.
The reason for this rule is that it ensures that the server has enough space on the C drive to do a full memory dump in the event of a crash.
Some useful links with more info about this subject are here:
Comparison of 32 bit and 64 bit memory architecture:
How to detirmin the page file size fore x64 servers
Going 64 bit with Exchange 2007 – (Shows what MS has done with their servers)
Bruce Sanderston’s understanding paging and memory etc
Hope this helps