Adding RAM (4 GB vs 8 GB)

Parallels Desktop 6, Windows 7, 15" MacBook Pro i7, 4 GB vs 8 GB Experience

If anyone is wondering if adding more RAM will have an impact on their Windows 7 virtual machine here are my initial observations. Initially I had 4 GB in my Mac. The virtual machine was set to use 1.5 GB of actual RAM leaving 2.5 GB for the Mac to use. When I started Windows 7 the whole machine would stutter, freeze, then come back to life several times. Usually after Windows 7 was running the virtual PC ran well, and as long as I did not tax the Mac with things like Aperture or other memory intensive programs it ran acceptably. I installed iStat Menu a while back and when the machine was having it's unresponsive spells the CPU was rarely more than 25% taxed. The RAM usage was 90%+ full and there was a lot of page-out memory (2 GB typically). Most of it was wired, I assumed because Parallels had allocated it and it was reserved for the PC.

WIth 8 GB in my machine I have upped the memory allocated to the virtual machine to 2 GB. Now when I start the virtual machine I am using around 3.4 GB wired and 1.7 GB active. Page outs are 0 of 64 MB. There are no longer unresponsive periods as Windows 7 boots up. The CPU pegs around 280% (of the i7 400%) when Windows 7 is booting (much higher than prior) likely because there is not a lot of swap file usage to slow things down. After it's finished booting and Windows is done updating the CPU is at 7% use (of the 400%).

prl_vm_app is using 287 MB RAM, Parallels Desktop is using 73 MB RAM. I don't see any large 2 GB files listed, so I do not know where the memory allocated to the VM is being used, but clearly it is removed from the memory available for the Mac.

Windows Experience (for what is worth) increased from 4.2 to 4.8. Real user experience is that Windows 7 is much more responsive and the Mac side is too.