Backups in Vista: which files to delete?

I'm running Vista Ultimate SP1 and using Windows Backup to an external HD
every night. Initially it did a Complete PC Backup and is now doing daily
backups of any files changed during the day. The problem is very simple:
the external HD is getting full, so which backup (zip) files can I delete to
make space? Are the backup files differential, ie increasing in size as they
backup all files changed since that Complete Backup, so that I can delete all
the files except the last one? Or are they incremential, ie each backup only
contains the files changed since the last daily backup, so they all have to
be kept?
Many TIA,
Tony.

Many thanks, Mark. That article is quite helpful, and from p47 it seems I
can safely let the nightly backups run without worrying about lack of space -
[quote]".....old restore points for System Restore are deleted when the
shadow storage limit on the live volume is reached, and old Complete PC
Backups are deleted when the limit is reached on the backup disk."
Otherwise I was thinking that I would have to delete all Windows Backups to
make space, and hope that it didn't crash while the new complete one was
done. Fingers crossed!
Tony.

"Mark H" wrote:

> http://download.microsoft.com/downlo...5db2/42_49.pdf
>
>
> "TonyB" <> wrote in message
> news:8BECD179-4CC9-4A21-9D43-...
> > I'm running Vista Ultimate SP1 and using Windows Backup to an external HD
> > every night. Initially it did a Complete PC Backup and is now doing daily
> > backups of any files changed during the day. The problem is very simple:
> > the external HD is getting full, so which backup (zip) files can I delete
> to make space? Are the backup files differential, ie increasing in size as
> they backup all files changed since that Complete Backup, so that I can delete
> all the files except the last one? Or are they incremential, ie each backup
> only contains the files changed since the last daily backup, so they all have
> to be kept?
> > Many TIA,
> > Tony.
>
>
>