Does built in Windows 7 backup perform differential (incremental) backups?

Question

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?

Solution

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.

Comments

[G-.]

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?

[A Dwarf]

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.

[Admin]

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?

[moritzebeling]

Anyone cares to comment on @user50272 comment?