Hello Kaktussoft,
excuse me ... i used the wrong term. It is a "systems image" (not mirror)
and yes, one created using the built in backup in Win 7.
I haven't seen or used Win 8 and so have no idea how different it is and do not
wish to lose the data and configuration I now maintain.
Keep Win7 and Win8 images entirely separate. I suggest you use free Macrium and use the bootable Macrium CD to do your imaging/restores. Name the images using your own scheme.
This is the "safe" way handle images. Image your Win7, then do your upgrade to Win8. Then image your Win8. You can keep the Win8, or go back to Win7 by doing an image recovery using the Macrium CD.
Then maybe you decide to give Win8 another try. That's no problem, again using the Macrium CD.
I'm still not sure your question was answered, or maybe you phrased it wrong.
So I'll ask the question differently using a scenario that an average Windows user might encounter.
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I imaged my Win7 system, using "Backup and Restore" within Win7 , then I upgraded to Win8. After upgrading to Win8, I then made a system image using the Win8 "Backup" function from within Win8.
I've found I don't like Win8. I want to go back to my original Win7 system by restoring my Win7 image. How do I do it? Will my Win8 system recognize my Win7 image, and restore it?
If not, do I need the bootable CD that can be created from within Win7 "Backup and Restore?"
Will that still work, or did making the Win8 image from within Win8 somehow make my Win7 image unusable?
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Those are the kinds of questions that should be answered before proceeding. Maybe more. I don't use Win8, so I don't know the answers. But if you get familiar with doing your imaging/restoring from a CD with Macrium, you don't need those answers. Personally, I use Ghost, but many here recommend free Macrium. I tested Macrium, and it works.
I don't recommend using the Windows-provided image/restore functions when there are more flexible free alternatives. The above example is a case in point. No such questions need answering if you cold image (that's imaging from a bootable CD) using something like Macrium or Ghost (there are others.) The learning curve isn't steep.
Hope I'm not coming off as pedantic, but I've been imaging many years, and found that following a few simple rules keeps me out of "gotchas". Anyway, I'm sure I'll be corrected if I'm off base.
This is whs's excellent Macrium tutorial.
http://www.sevenforums.com/backup-restore/43219-image-your-system-free-macrium.html