I don't know if this was addressed before but..........

I just put together a new sys with Win7 64bit and I'm slowly of getting used to this OS.

However, after a few days, I discovered that my Windows folder is over 16 gigs after the intial install of only just a few gigs
I have also learned that this is about normal.

My question is why is this? Why does win 7 suddenly expand to 16 gigs a couple of days after install?
This is with all unnessay files cleaned out and the disk defraged