4 GB of RAM installed but only 2.97 GB usable. What gives? [duplicate]

4 GB of RAM installed but only 2.97 GB usable. What gives? [duplicate]

I just bought a used MacBook on eBay that came installed with 4 GB of RAM. The first thing I did was installing Windows 7 using Boot Camp. Here's where it gets weird. When I finally booted it up in Windows 7, I checked the Computer properties, and it said that there were 4 GB of RAM, but only 2.97 GB is usable. Why is that? Is there anything I can do about this?