backup file size—SD vs. Time Machine

[jotaro]

Here's another issue concerning backup, it seems to me:

SuperDuper duplicates what I am backing up, which means the backup file on the external hard drive will be about the same size as on my hard drive.

Time Machine, however, keeps adding to the backup hard drive. Let's say I made edits every day to a 2 GB movie file. Time Machine adds another 2 GB file to the backup disk every time I make an edit. If this is correct, the back up gets huge fast, far exceeding the size of my hard drive, which is 250 GB. Does this mean I should think about buying an external drive for Time Machine backup that is 3 or 4 times the size of my hard drive?? Does Time Machine recognize limits of back up disk and automatically lop off oldest files to make room for new ones?

jotaro