Is an image backup useful if I need to restore to a different machine?

What's an image?

When it comes to backups, the term "image" can mean either of two things:

• Every byte of every file that is on the hard disk, including the boot sector, the operating system, all of your installed programs, and of course, all of your data. In this sense, it is an "image" of all of the data on that hard drive.

• Every byte of every sector on the hard drive, whether it's currently in use or not. Coincidentally, this also contains all of the data on the drive as well as whatever was in all of the unused sectors.

For purposes of our discussions here, the difference doesn't matter. You may hear them referred to as images, clones, or copies, but as long as every bit of data is there, regardless of what it is, I'll simply refer to it as an "image backup."

Image backups are typically specific to the machine

When you take an image backup of your C: drive, you're backing up all of Windows in addition to your data.

That means the backup contains Windows as well as all of the machine-specific drivers and settings for that particular machine.

The net result is that an image backup of your system drive is optimized so that you can simply restore it back in its entirety and it's ready to go.

When the hardware changes, things get ... interesting.

Restoring to different hardware: worst-case scenario

Let's assume that the hardware has changed dramatically. Completely different computer from a completely different manufacturer with different ... everything.

If you've used the correct backup software to create your image, you'll still want it.

Here's how:

• You'll install Windows on your replacement machine from scratch. This will allow Windows to configure itself for the new hardware. (Perhaps a copy of Windows will even be pre-installed.)

• You'll reinstall the applications that you use. Perhaps some might be pre-installed, depending on where the machine came from, but the worst case is that you'll need to install or reinstall any that you need from scratch from original installation media.

• You'll restore your data from the image backup.

An optional approach to that last step is to install a second hard drive, or use an external hard drive, and restore the image backup to that. That way, once running, you can simply access all of the files that it contained.

The reason that image backups are so powerful is that they contain everything; you don't even have to think about what to backup. You may not need the entire backup when restoring to a new machine, but you'll still want it for your data files.

Because everything that was on the drive is there in the backup.

Everything.

Not-quite-as-bad-case scenarios

Occasionally, an image backup can be used very close to its optimal way: restore the complete computer directly from the image.

One scenario is:

• Restore the hard disk from the image backup.

• Reboot into the restored copy of Windows.

• Windows notices that "a few" things have changed and adjusts itself accordingly.

That's perhaps the best-case scenario for new hardware. It might be followed by some partition management if the hard disk that's being restored to is a different size than the original, expanding the restored image to take up all available space.

Another scenario that I've heard of that works occasionally:

• Restore the hard disk from the image backup.

• Boot from your Windows installation media.

• Perform a "repair" install of Windows.

• Reboot into the restored and fixed copy of Windows.

Naturally, that assumes that you have your installation media available.

And finally, a third scenario is emerging:

• Restore the hard disk from the image backup.

• The backup software that you're using specifically supports restoring to different hardware and as it performs the restore, or perhaps after, it attempts to make the necessary adjustments.

• Assuming that's successful, reboot into the restored and fixed copy of Windows.

I don't have any direct experience with this scenario and remain somewhat skeptical that all possible hardware configurations could be handled, but the goal is laudable and promising.

Image backups: a great safety net

As I mentioned above, because an image backup contains everything on your hard drive, it's nearly the perfect safety net. Even if you can't use it for a complete restore of that image by definition, it contains every file on that hard drive. Without needing to remember what to backup, you have everything and can recover your data no matter what.