We have an ASP.NET application, built around MonoRail and NHibernate, and I have noticed a strange behavior between if running it with 64-bit mode or 32-bit mode. Everything is compiled as AnyCPU, and runs fine with both modes, but the memory usage differs dramatically.

Look at the following snapshots from ANTS:

32bit_snapshot: enter image description here

vs

64bit_snapshot: enter image description here

The usage scenario for both snapshots are pretty much equivalent (I have hit the same pages on both runs).

Firstly, why is the Unused memory so high in 64-bit mode? And why would unmanaged memory be 4 times the size on 64-bit mode?

Any insight on this would be really helpful.

asp.net .net memory-management iis-7.5
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