It’s not a question of “allowing”.
By definition, restoring a full image backup will completely overwrite everything that exists on the hard disk, replacing whatever was there before, no matter what it was.
So, sure, the previous operating system, along with everything else on the hard disk, will be overwritten and replaced with the contents of the image backup.
The real question is: will what you’ve just restored then work?
Most of time, the answer is a very short “no”.
I’ll explain why that is.
What your backup is and isn’t for
What you’re asking is an extremely common question – so common that I discuss it in each of my “Saved!” series of books on backing up.
Since an image backup contains the entire system, many people would like to use it when moving to a completely new machine. The concept is simple: restore that image backup to a new or replacement machine, and carry on where you left off.
That’s not what image backups are for.
Image backups are a snapshot of a specific machine, and are designed to be used in either of two scenarios:
- Restoration of the entire system to a known good state on the same machine – for instance, in case of malware infestation.
- Restoration of the entire system to a replacement hard drive on the same machine, as in the case of a hard-drive failure.
Because image backups contain everything on the machine, they are also very conveniently used for one additional purpose:
- Restoration of specific files, typically data files, onto any machine, anywhere, at any time (even the files you didn’t know you needed), because the backup contains everything.
Restoring a complete image backup to different hardware isn’t on the list.
Windows configures itself for your machine
When you install an operating system, the set-up program goes through what appears to be pretty much the same sequence on every machine: you enter the product key, type in a little information, tell it what machine name you want and perhaps the time zone, and pick an administrator password. Then, set up goes to work, showing a progress bar or some
propaganda information about the benefits of the operating system you’re installing and how wonderful your life together will be.
What happens behind the scenes is significantly more complex.
Every machine is different from every other machine, and it’s during installation that those differences are accommodated.
Once it’s set up, Windows is highly customized to the specific characteristics of your specific computer.
What your backup image contains
The problem is that a backup image of any machine contains a version of Windows specifically configured for the computer on which the backup was taken.
It has drivers and settings for that hardware, and has generally been customized for that hardware. Attempting to restore Windows to a different machine means it won’t have the proper configuration it needs to run. Depending on just how different the hardware turns out to be, you may experience any of the following:
- Windows won’t even boot. This is fairly common.
- Windows may “run”, but will be unstable or present an assortment of error messages.
- Windows may appear to run, but at some point later you may discover instability or other problems that defy explanation.
I suppose in some cases, it could just work… but it’s not something you should count on.
Restoring to a different machine might work if….
It is possible for the scenario to work, but several conditions must be met.
- The motherboard on the two machines must be similar. What does “similar” mean? There’s no real definition: motherboards often have a variety of hardware that require a specific set of drivers in order to work properly. Ideally, the motherboards would be identical.
- For individual devices that are not identical, they, too, must be “similar”. Once again, the degree of similarity depends on the specific device and the capabilities of the driver installed.
- For those individual devices that are not even similar, then they must be optional, meaning that the system will run properly without the device.
If those conditions are met, maybe it’ll work.
And it’s a huge if.
It’s possible that Windows will be able to boot, notice that some non-critical hardware has “changed”, go through the process of updating itself (perhaps asking for driver or installation disks), and actually run.
What you’re suggesting is actually a very common approach to installations that have a large number of identical machines, but the further you stray from truly identical machines, the lower your chances are of this approach working.
Windows on a new machine
When replacing a machine, the more correct sequence is:
- Install Windows from scratch if it didn’t come with the machine to begin with.
- Install your applications from scratch.
- Restore your data files from your backups.
- Make a backup image so you don’t have to repeat steps 1 through 3 again should you ever need to restore this machine to its initial condition.
If, on the other hand, the failure does not involve replacing your entire machine, then the process is much simpler:
- Restore the entire machine from your image backup.
Because that’s exactly what a backup is for.
There are tools…
Before we give up on the concept entirely, I do want to point out that there are tools that can sometimes help in situations where an install from scratch is something you really want to avoid.
Redeploy is a feature available in some versions of my recommended backup program, Macrium Reflect, that specifically attempts to restore an image configured for one machine to another. I’ve used this once or twice successfully to move a backup image of a friend’s computer onto a virtual machine (another case of completely different hardware). Other companies, particularly those with backup programs, have additional solutions to address this scenario.
While not quite the same, several companies provide utilities that promise to transfer programs and settings from one installation of Windows to another. Quite often this is what folks are looking for when they think of using an image backup to transfer setups between computers.
The solutions I’ve seen in both realms are not free. In addition, the problem being solved is incredibly complex. If you do go this route, I would proceed with caution, which means backing up early and often as you perform the transfers.
I much prefer the clean install approach. The result is typically a significantly faster and more stable system.