Time machine and split plain disks

How does Time Machine handle the virtual drive when it is set to plain and 2 Gig chunks? Will it backup the whole virtual disk or only those chunks affected by the changes? As you may guess I am shooting for the last alternative.

If so question two. How many chunks will be changed within a typical windows session with no new programs installed, just some outlook work and nothing else too much changed. Any experience or estimated guesses?

Thanks in advance