90GB used on my C: drive and 157GB used on my external backup.
I’m using Windows backup. It’s scheduled once per week. Shouldn’t my backup mirror the current state of my C: drive? I formatted the external drive when I purchased it and it has only been used for backup, no other data.
Does backup make additional copies of certain files every time its run? I thought that it just looked for any changes since the last time and wrote those to the existing image. If I ran a backup on sunday and once complete I shut down my computer and didnt use it till next sunday and immediately ran it again, shouldn’t it say there is nothing to back up?
Yes, unless you tell it otherwise (or it detects that it is running out of backup media space) Windows Backup will store a now “system image” each time it is run. This is an image of Windows itself, and even if you have done nothing to it yourself, it often changes due to security updates. It will not store an infinite number of these, but by default it will not usually delete the previous one when it stores a new one. I think how many it stores depends on how much free space is on the backup media. As far as your own data files go, I think you are right that it will only store new or changed files on each backup, but it does not delete the old versions from the old backup (until space becomes tight), so this still takes up increasing amounts of space.
If you double click on the backup folder on your external drive, you will be given the option to “Manage space used by this backup”, and this will allow you to delete obsolete backups of data files, and you can also set backup to retain only one system image. However, it is probably best not to do this unless you are going to need the space on your backup media for some other good purpose (and if you do decide to delete some of the backed up data, do it with care).
Windows 7 isn’t nearly that large, its size is just mis-read by Explorer. More specifically, the WinSXS folder reads as somewhere between 8-9 GBs, but in reality it’s only a few MB. (The vast, vast majority of “files” in there are actually NTFS hard-links to other files, and don’t actually use up any disk space. Explorer double-counts those.)
Windows 7 backup program is designed to basically fill the space its given. If it has lots of space to work with, it’ll store a new backup of a file every time a file is changed (so you can “rewind” the file to a specific point.) That’s by design. If you want it to use less space, you need to give it less space to use. For example, by partitioning your drive and putting it on the smaller partition.
It’s not a matter of “being efficient”, it’s a matter of “Windows 7 backup doesn’t do what you want”, or “Windows 8 backup makes assumptions that don’t apply to your situation” (the assumption it can use 100% of the space its given.)
It is not a question of inefficiency. Like I said, you can easily turn off this behavior, and have it delete the old system image each time it stores a new one. However, if your last backup happened after Windows got corrupted by malware or something, you would regret this, so it is better not to do it unless you actually really need the space for something else.
The short answer is backups have to keep old versions of files. They’d be quite useless if they only kept the latest version. If your disk got corrupted and you only found out later, you’d only have a corrupted backup.
As to keeping whole images, I don’t think Windows Backup does that all the time, it only keeps track of changes (“incremental” backups). Full backups would take too much time and space.