Is my RAM used when Parallels isn't running?

Hi there. I am brand new to Mac and brand new to Parallels.
My new MBP just arrived yesterday and I installed Parallels 6 and Windows 7. I allocated 4GB of the available 8GB for parallels/windows to use.
So my question is, does this mean my mac osx only has 4gb of ram to use now? Or does is still have 8gb and only when parallels is running it has 4gb with parallels using the other 4gb?
Sorry if this seems like a dumb question, it's all very new to me at the moment.
Thank you so much!