[adamfishercox]

As per this image (the "Time Machine keeps..." section of the window):


It's kind of confusing. I'm assuming what it says is that TM will keep 24 hours of backups, at which point it compresses those into a day's backup, after a month of daily backups it compresses it into a monthly backup. Am I right?

It could be misconstrued to say that if you choose hourly backups, your backups will be deleted after 24 hours; if you choose daily they'll be deleted after 30 days.

[Brass]

Time machine does not compress backups (due to the way it uses multiple hard links compressed backups would be unmanageable).

It simply deletes hourly backups that are more than 24 hours old, etc.

[adamfishercox]

What the hell is the point of a backup system that deletes your backups after 24 hours. What if I want a file from 3 days ago?

[Art Vandelay]

It's still there. It deletes the hourly backups over 24 hours old but when it does that, it coalesces the changes into a single daily backup. The same goes for days after 30 days.

[adamfishercox]

Oh. That's what I asked. Apparently Brass misconstrued it as I thought one could (not meaning that as an offense, Brass). Apple should rewrite that little section.

[Art Vandelay]

I think he took your use of the word "compress" literally. It does not compress the data.

[Brass]

No, I think you misconstrued me. No surprise, I could have been clearer.

I neglected to add that one of the hourly backups each day becomes a "daily" backup and doesn't get deleted after 24 hours. One of the dailies each week, becomes the "weekly" backup, and doesn't get deleted after a week.

None of the backups get compressed, ever, by time machine.