But I'm not sure what details the ComputerWorld.com article thinks Apple is keeping close to the vest. The Time Machine preference pane (in System Preferences) provides, in 32 words, a very nice summary of how it works that is detailed enough for the vast majority of users.
I'll just <
link to the article> then, and quote the specific passage:
Inside Leopard's Time Machine: Backups for the rest of us (excerpt from page 5):
Finally, it is worth mentioning that Time Machine is very smart in how it determines what to delete when a disk begins to get full. It doesn't simply delete the oldest backups and all their files. Instead, when Time Machine deletes an older backup, it deletes only the files that were unique to that backup (i.e., files that no longer exist anywhere in the file system).
Time Machine also doesn't delete just the oldest backups. While it does keep many recent backups at frequent intervals, it also keeps a range of older backups from a wide range of dates, letting you browse as far back in time as feasible. Exactly what computation goes into determining this approach isn't quite certain (and Apple may have a competitive advantage if it chooses to keep some of Time Machine's secrets close to the vest), but in early testing, it does seem an effective solution.
edit: note that that comes from a very early review, dated October 29, 2007.
