Paging in OS X with ample available memory

I've noticed that when I provide my VM (Windows 7, Bootcamp, VHD, Windows 8, regardless) with roughly 3GB of physical memory (or more) and 256MB of graphics memory, my host OS starts using the swap file pretty much right away. This happens even right after a reboot, then startup Parallels and a VM. I have 16GB of physical ram, with a lot still free (not "reserved" or in any other type of use), but Parallels seems to behave like a 32 bit application and use virtual memory when it approaches the 4GB limit. Is there a reason for this, or something I can do to make sure that Parallels uses the entirety of memory as physical memory whenever possible?