I have been thinking about a backup strategy (BUS) for a while and so now I am thinking about Time Machine (TM) and its practical imports for a BUS. If I understand correctly, TM backs up (unless disabled, not connected) every hour until it reaches one day and then the last backup becomes the backup for that one day, but the hourly backups for that day are not differentiated after 24 hours because the next/current day becomes the source for the hourly backups. Likewise, the after 7 days the backup becomes a weekly backup and the daily backups for that week are not differentiated. This pattern follows up to the one month marker. So here is my question. TM seems like a rolling backup which protects only against immediate failure, but is inadequate for archiving. E.g., if I wanted to restore a file from day 2 but am now on day 9 and the file was changed between day 3 and day 7, then that file no longer exists because the file from day 2 becomes superceded by the file changed between day 3 and 7. That is, the file from day 2 is overwritten by the later form of that file when the TM backup switches from daily to weekly. Am I wrong or do I understand this correctly? If this is so, then it seems that some other backup solution is also necessary for archiving unless one does not mind either losing archival data or buying a lot of hard drives. At the very least, the amount of space TM may require for backups mandates that if one does not purchase and use new HDDs then one will eventually have to remove old files to make room for new file backups.