HT1427: Mac Basics: Time Machine backs up your MacLearn about Mac Basics: Time Machine backs up your Mac
Currently Being ModeratedMay 4, 2012 1:24 PM (in response to tevfrombc)
As long as it is still on your Hard Drive, it will be on the Time Machine. If it deletes the oldest backup and discovers that your file is not on what is left, it will back it up again.
Currently Being ModeratedMay 4, 2012 2:47 PM (in response to tevfrombc)
To oversimplify slightly, each Time Machine snapshot has a link to every file that hasn't changed since the last backup. As long as at least one link to the file remains, it's still in the repository, even when older snapshots are deleted.
Currently Being ModeratedMay 4, 2012 3:57 PM (in response to tevfrombc)
If it's only updating files that have changed, how is it ensuring that my unchanged files are backed up after it deletes the initial, complete backup when my external hard drive gets too full?
There's a nice explanation in this section of Pondini's user tips:
Currently Being ModeratedMay 7, 2012 5:03 PM (in response to jsd2)
Thank you all that was VERY helpful. In particular, the Pondini article was exactly the kind of technical detail I was looking for and couldn't find on the apple site. Thanks again everyone!