Do processes on VMWare/Parallels effect OSX performance?

You haven't told us what applications you may be running simultaneously so it's tough to say. If you're doing something like ripping a DVD on Handbrake and playing a game on MS Windows at the same time with only 4GB of RAM you're going to see a performance hit. However if you're just web surfing on Safari and running a game the performance should be OK. Please try to be more specific when asking questions, we can't always read your mind.

Personally I run VM Ware but I don't game and most of the time I don't tax my Core 2 Duo system. With 6GB of RAM it flys though.

Should be fine. If you aren't totally satisfied with the performance a simple RAM upgrade would help a lot and RAM is inexpensive right now.

Processess running in Parallels or VMWare take up memory and CPU usage-- while they are running -- like any process running under OS X does. On top of that, having a virtual machine running also has the overhead of the guest operating system itself (both in processor and memory use).

However, both Parallels and VMWare do have settings that let you favor performance of the VM or performance of OS X, and you can control memory usage and CPU cores available.

Further, Parallels and VMWare have no impact on the performance of OS X when you aren't running a VM.

JD - Great explanation... thanks for the post!

You do know Warcraft is available for Mac?

This is why I went and bought a new mbp because my 4gb of RAM in my old mbp was not enough to run Win 7 on parallels. I have some work to do that requires windows so that is why I got parallels which I love but it was a resource hog. Now that I have my new mbp I can run Win 7 and listen to my itunes without any slow down at all. So to answer your question, using parallels does affect your computers performance if you don't have enough RAM and a slow processor. I don't have that problem anymore but I had to pay for it with a new computer. Yea I know boo hoo right?!