Originally Posted by easysurfer
Interesting story about time machine. My understanding (through bulletin boards) is that it looks awfully similar to Rollback Rx. In fact, on a board, someone from Rollback said that contractors who were working for Rollback at the time had sticky fingers (or more precisely, sticky keyboards) and took a lot of the code. Another difference is that Rollback is not free, but time machine is offered as totally free.
Time Machine's backup mechanism is home-grown at Apple. It uses a special modification to the HFS+ file system that allows hard linking of directories as well as files, through some interesting hacks to the inode structure of the file system. (blah,blah, blah... :-) ). Backups are done by copying changed files since the prior backup into the hard linked directory tree, which gives a result that looks like a whole new directory tree with the current time stamp while only using the space needed to copy the changed files. The filesystem and backup service track and accumulate the set of changed files since the last backup.
The display trickery (the cosmetic stuff that sold Steve Jobs on it) is done via stacked transformation matrices in the window system. All the regular windows and panels get translated off screen, with a snapshot of the Finder (or Mail, or other Time Machine aware app) held onscreen until the app has its view into the selected archived files ready.
Rollback Rx is an incremental sector level backup and redirection scheme for Windows. It lives at a very low level, below the file system. That gives it the ability to recover an unbootable system by redirecting to an older set of disk content, sort of like a saved version of the system that might still be bootable.
The different mechanisms involved are best understood with a minimum of two pints of Guiness.