Time Macine, "what's backed up?"

I have a fairly deep history with *nixes, but I can't for the life of me figure out what the ****** TM is doing to figure what ought to be backed up. One time it's 600K, the next it's 1GB. I've looked at the raw backup data, and there's crap in there I haven't touched in months. I could spend more time to figure it out, but thought I would take the cheap route first and see if anyone has already spent the time and knows...

By default Time Machine backs up everything on your main hard drive. It then does incremental updates, backing up whichever files had been updated in the last hour. Over time, these updates are then consolidated into daily backups, then weekly, then monthly.

If I understand correctly, TM also uses hard links so that unchanged files are not backed up and thus not taking up space on the back-up drive while making it appear as if each backup is a full backup.

Kash said:

By default Time Machine backs up everything on your main hard drive. It then does incremental updates, backing up whichever files had been updated in the last hour. Over time, these updates are then consolidated into daily backups, then weekly, then monthly.

Click to expand...

including OS files and programs?
full 50gb will be full 50gb?

Unless you specify otherwise, yes. You can restore your system with a Time Machine backup, so it needs to save every file.