okay, so I've tried searching for this on google, and on here, but since I'm not entirely positive what to search for I'm not getting relevant results, so thought I would just ask. Also, I decided to post this in this section of the forums, because it seemed the most appropriate even though it deals with a desktop as well as a laptop.

I currently own two macs: MacBook Pro Laptop and one of the older, white Apple iMac 17". I am selling both of them and trading up to a new MBP in about a week. I am currently backing up my BMP with Time Machine (to an external drive) so when i get the new MBP i can transfer all my old stuff onto the new one.

When i got my MBP I copied my iMac onto it, and then cleaned off some files I didn't need to use every day to make space, so I know that the old iMac has some older info on it that my MBP does not, and I'm wondering if there is a way that I can back it up and then somehow cross-reference all the information so i can have one copy of everything instead of multiple copies or the stuff they both have.

I know that sounds kind of complicated, but do you understand what i'm saying? Two computers with probably 80% of the same info, and I want to be able to compare the two so instead of having two copies of two computers that are 80% the same that i could have a whole copy of one computer and then just the 20% different information from the older one.

thanks in advance to anyone who can help!!