prl9 memory usage (OSX)

When using prl version 8 my 3GB VM used 3GB OSX memory (actually a little more, 3.1 or 3.2GB).

Since upgrading to prl version 9, my 3GB VM even when running lots of stuff, is using just 550MB of OSX memory. Inside the VM windows says I am using just over 2GB.

This is great, but how is it accomplishing this feat?
Is it a known improvement between 8 and 9?

 

My 4GB VM uses the following (according to Activity Monitor):
Real mem: 3.32 GB
Private mem: 4.12 GB
Shared mem: 523.7 MB
Virtual mem: 4.29 GB

Maybe you're only looking at Shared mem.

 

Inspecting the process, it says:

Real: 432MB Virtual: 6.15GB Shared: 70MB Private: 3.13GB Virtual Private: 3.29GB

or from top

PID COMMAND___ %CPU TIME____ #TH_ #WQ #POR #MREG RPRVT RSHRD RSIZE VPRVT_ VSIZE PGRP PPID STATE UID FAULTS
686 prl_vm_app 32.0 13:31.91 59/2 1__ 323_ 2250_ 3207M- 243M+ 432M 3367M- 6295M 482 567 running 501 16056406


Resuming the VM, used memory goes up by 2.25GB yet RPRVT suggests it is using 3.2GB memory and RSIZE only 432MB resident

After doing some research into the difference between RSIZE and RPRVT I have decided that, no one really knows what they are
Some say RPRVT is the one to watch while others say RSIZE. Some say RSIZE should be the sum of RPRVT and RSHRD but it clearly isn't the case here.

Conclusion:

pr_vm_app is using SOME memory
and I think I will leave it at that.