System images are complete backups of everything on your PC’s hard drive or a single partition. They allow you to take a snapshot of your entire drive, system files and all.

Windows, Linux, and Mac OS X all have integrated ways to create system image backups. There are sometimes good reasons to do this, but they shouldn’t be your regular backup strategy.

What is a System Image?

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A system image is a file — or set of files — that contains everything on a PC’s hard drive, or just from one single partition. A system imaging program looks at the hard drive, copying everything bit by bit. You then have a complete system image you can copy back onto a drive to restore the system state.

The system image contains a complete snapshot of everything on the computer’s hard drive at any given time. So, if you have 500 GB of space used on a 1 TB drive, the system image will be about 500 GB. Some system image programs use compression to shrink the system image’s size by as much as possible, but don’t count on saving much space in this way.

Different system image programs use different types of system images. For maximum compatibility, you should use the same tool you used to create the system image to restore it. Windows itself creates system images that contain multiple files with the .xml and .vhd file extensions. System images are just one of the many back up tools included in Windows.

System Images Aren’t Ideal for Normal Backups

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System images aren’t the ideal way to create normal backups of your computer and its files. System images are very large, and they contain files you really don’t need. On Windows, they’ll probably include tens of gigabytes of Windows system files. If your hard drive crashes, you can always just reinstall Windows — you don’t need backup copies of all these files. The same goes for program files. If your hard drive crashes, you don’t need an image of your installed Microsoft Office and Photoshop program files — you can just reinstall these programs on a new Windows system.

System image backups will capture files you can easily redownload and reinstall as well as files you don’t care about. You can’t control what is and isn’t backed up — you end up with an image containing everything on your hard drive.

Because so much data has to be backed up, a system image will take a much longer time to create than a smaller, more focused backup. It will also be harder to import on another computer. If your entire computer dies, you won’t be able to just restore a system image that was created on another computer — your Windows installation won’t run properly on different hardware. You’d need to reinstall Windows anyway.

This doesn’t just apply to Windows. Macs include an integrated way to create system images, and Apple advises you only restore system files on the same Mac the backup was created on.

For typical backups, you should just back up the files that are actually important to you. If your system ever goes down, you can then reinstall Windows and your programs and restore your personal files from the backup. Use File History to do this on Windows 8 or Windows Backup to do this on Windows 7.

When You Should Create a System Image

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System images can still be useful. For example, let’s say you want to upgrade your computer’s hard drive — maybe you’re upgrading from a slower mechanical hard drive to a speedy solid-state drive. You can create a system image of your computer’s hard drive, swap the drive out for an SSD, and then restore that image to the SSD. This will migrate your entire operating system to the SSD. Of course, if both drives can fit in your computer at once, you may be better off using a system imaging program to copy the contents of your hard drive directly to the SSD rather than creating a system image backup and then restoring from that, which will take twice as long.

These types of images can also be used by system administrators, who could roll out a standard system image on different PCs across their network. A server or other mission-critical computer could be configured and a system image created to restore the software to that specific state.

If you’re a typical home user looking to back up your files, you probably don’t need to create a system image.

How to Create and Restore System Images

To create a system image on Windows 8.1, open the Control Panel, navigate to System and Security > File History, and click the System Image Backup link at the bottom-left corner of the window. On Windows 7, open the Control Panel, navigate to System and Security > Backup and Restore, and click the Create a system image option.

You can then restore these backup images using the Advanced Startup Options on Windows 8 or the System Recovery option on Windows 7. These can be accessed from a Windows installation disc or recovery drive.

On a Mac, you can use Time Machine create and restore system image backups. Time Machine backs up system files as well as your own files, and you can restore a Mac from a Time Machine backup from Recovery Mode. On a Linux PC, you can use the low-level dd utility to make an exact copy of a drive and restore it later.

Acronis True Image and Norton Ghost are popular third-party disk imaging tools you can use for this, too.

While developing Windows 8.1, Microsoft removed the “System Image Backup” option from the user interface and forced people to access it from a PowerShell window. After widespread complaints, Microsoft restored this option to the graphical interface.

Microsoft’s motive was pretty clear here — average PC users shouldn’t be distracted by system image backups and should just use a simple backup solution like File History. Microsoft eventually restored the graphical option to make people happy, which is fine — but they were right that most Windows users shouldn’t use it.

Image Credit: Phillip Stewart on Flickr

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Chris Hoffman is Editor-in-Chief of How-To Geek. He's written about technology for over a decade and was a PCWorld columnist for two years. Chris has written for The New York Times and Reader's Digest, been interviewed as a technology expert on TV stations like Miami's NBC 6, and had his work covered by news outlets like the BBC. Since 2011, Chris has written over 2,000 articles that have been read more than one billion times---and that's just here at How-To Geek.
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