32 vs 64 bit

I ran  R on an AMD Athlon 64 with a 32 bit Linux (by accident, I moved 
the hard disk from another machine). Now, after install 64 bit Linux and 
64 bit R, I am finding some of my R tests are quite a bit slower, I 
think because memory demands cause a lot of swap. Does anyone know if 
extra memory usage would be mainly because of R itself, or is there a 
lot of extra memory demand because of the OS, windowing system, and 
other apps?

Paul Gilbert