i am actually talking about the "iphone back up".
if want to move my backup to my mac, how can i do it?
currently its on my pc.
It's pretty simple. Once you plug it into the mac you can authorize that computer with your iTunes account and transfer all your purchases from the phone to the mac. It will also automatically do a backup of your iphone. Just transfer all your stuff like music, videos or pics to the new mac and you're good.
In answer to your question as to what is backed up:
Backups contain the following:
call logs, recent call list, call timers, voicemails
settings
saved app data (like saved games and app settings - however, this is partially up to the developer to implement)
text message history
notes (if not being synced with notes on your computer)
stocks
weather cities
camera roll photos (no other photos)
app locations/placement (on 3.0 ONLY, saves what pages and locations you kept your apps)
It does NOT backup:
Contacts
Calendars
Emails
Apps
Music
Videos
Photos
Ringtones
(Basically everything that you should have saved on your computer or mail service and you can resync).
See this link for more info:
http://support.apple.com/kb/HT1766