The question that I get asked a lot currently is am I running 32bit or 64 bit Windows and what does all this mean.
On a 32 bit version of Windows you are restrcited to 4GB of ram as that is all Windows will recognise.
64 bit Windows recognise more than 4GB of ram , ideal for those applications or systems that require memory.
The following links can answer many questions on 32bit and 64 bit Windows versions.
What is the difference between 32bit Windows and 64bit Windows
Is my computer running the 32 bit or 64 bit version of Windows