Snapshot file size

HI,

I have a doubt on snapshot let's say i have a VM  win2003 with the vmdk 40GB so out of that 10GB is full remaining space i  have is 30 GB  if take a snapshot delta files will be created for each  snapshot.

so these delta files will take the space of datastore  ok. so these delta files can grow Maximum to 30GB which is free space i  have on vmdk or they can grow amount of size let's say my datastore size  is 500GB.so how my delta files takes the space from datastore.

Thanks..