I have win 7 scheduled to backup every Sunday, it's only looking at one of my drives at the moment and is backing up to an external HDD. It's a 1TB drive so should take quite a while to fill but the amount of time the backup takes makes me think its taking a fresh copy every time.

It's now 21:34 and I think backup started at about 19:30. It did a full backup earlier in the week of approx 200GB. Is it copying the whole lot again? Or is it just taking its time checking for differences?

1 Answer 1


Windows 7 Backup is a block based file backup.

This means each block in a file is examined and if a duplicate already exists on the last backup, and this is the important bit, even if from a different file, that block is not saved. Quite good :)

The first backup is always a full backup. The following backups will only save changed blocks. Disadvantage is you cannot manage your backups individually.

  • ah! Very clever. So the time delay is due to re-examining all the blocks. Do you have a link to some futher reading on this?
    – G-.
    Oct 25, 2009 at 22:07
  • ermm.. will have to search for that. Been a while since I last read about it. Will add a comment with the information
    – A Dwarf
    Oct 25, 2009 at 22:18
  • 5
    Incremental here: social.technet.microsoft.com/Forums/en/windowsbackup/thread/… Block based incremental here: social.technet.microsoft.com/Forums/en/w7itprogeneral/thread/… There's somewhere, on one of the developers blogs or something, a detailed explanation of the Backup features. That's where I remember reading about it the first time during the beta times. I just can't locate it right now. But those two links should be enough.
    – A Dwarf
    Oct 25, 2009 at 22:29
  • 3
    So... If you deleted something prior to the last backup (therfore blcks have changed) does that file get removed from the backup image as well?
    – user50272
    Jan 8, 2011 at 5:23
  • Anyone cares to comment on @user50272 comment?
    – Boris_yo
    May 26, 2014 at 10:27

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