I have 2 MacBooks (with 3 user accounts total) that I would like to back up using Time Machine to a 1 TB hard drive. I'd like to dedicate 700 GB or so of the hard drive to the backups and have the other 300 GB to use for other things. Do I need to create one partition for each computer, or one partition for each user account, or Can I back up all the computers to one 700 GB "Time Machine" partition?