Restoring a backup is the moment your backup strategy is tested. You have an .img file made with Win32 Disk Imager Read, a card that has failed or needs to be replaced, and a need to get back to a working system quickly. The restore itself is a Write operation, but the stakes are higher than a first-time flash, because you are often restoring under pressure, and a mistake now can overwrite the wrong drive or destroy the only working copy of something else.
This guide is for anyone who made a backup, or inherited one, and now needs to put it back onto a card. It covers checking the backup file, choosing a suitable destination card, writing it correctly, and testing the result before you rely on it. It assumes you have a Windows computer, the backup file, and a destination card at least as large as the original card the backup came from.
The central warning of this guide cannot be overstated: restoring overwrites the ENTIRE destination drive. Everything on that card will be lost, including partitions you cannot see. Double-check the drive letter every time, and never restore over a card that holds data you have not backed up elsewhere, even if you are in a hurry.
Before you start
- Restoring wipes the ENTIRE destination card. If the destination card holds anything you need, copy it elsewhere first, or use a different card.
- The destination card must be at least as large as the original card. Cards sold as the same size can differ by a few megabytes, so a restore to a slightly smaller card can fail near the end.
- If the backup is compressed as a .7z or .zip file, decompress it to a plain .img file first. Win32 Disk Imager cannot write directly from a compressed archive.
- Keep the backup file safe during the restore. Do not restore from the only copy on a drive you are about to format, and do not delete the backup until the restored card has been tested.
Before you restore, confirm what the backup actually contains. Check the file name, date, and any notes you made when you created it, and confirm the file size is plausible for the original card. A backup file that is far smaller than the card it came from may be a compressed archive you forgot to decompress, or an allocated-partitions image, which is still valid but restores differently in terms of layout. Knowing which kind you have avoids confusion when the restore behaves unexpectedly.
Step by step
1. Locate and prepare the backup file
Find the .img file, and if it is compressed, decompress it with 7-Zip to a plain .img file on a drive with enough free space. Check the decompressed size against your notes or against the original card’s capacity. If the backup is on cloud storage, download it completely before you start, because a partial download that writes successfully will not boot.
2. Insert the destination card and note its letter
Insert the destination card, wait for Windows to recognise it, and note its drive letter in File Explorer. If Windows offers to format the card, choose Cancel. You are about to overwrite the card completely, so formatting first is unnecessary. If the letter you expect is missing, reseat the card or try another reader.
3. Open Win32 Disk Imager as administrator
Run Win32 Disk Imager as administrator, click the folder icon, and select your .img backup file. Confirm the Device drop-down shows the destination card’s letter, not the letter of another drive, a USB stick with data on it, or an external hard drive. This check is the most important step in the whole restore.
4. Write the backup and eject safely
Click Write, read the confirmation dialog, and confirm only if the drive letter is correct. Wait for the success message without removing the card or letting the computer sleep. When it finishes, use Safely Remove Hardware before removing the card, because Windows may still be flushing the final writes.
5. Test the restored card before relying on it
Put the restored card into its target device and boot it. Check that the system starts, the main application runs, and recent data you expect is present. If the device is a Pi, give first boot a few minutes, and check that the filesystem has the expected size. Only after this test should you consider the restore complete and the old card disposable.
6. Make a fresh backup of the restored system
Once the restored card is working, make a new Read backup of it, especially if you changed anything during recovery, such as passwords, network settings, or software versions. That fresh backup becomes your new baseline, so the next failure does not send you back to an older state. Label it with the restore date and a note that it came from a restore.
Where to keep the backup
A backup only helps if it survives the card it came from, so copy the finished .img file off the computer you flashed from. A dedicated backup drive (Sponsored) works well for large images, and you can also keep a second copy in cloud storage such as pCloud if you want an off-site copy. Label every file with the device, date, and contents before you upload it.
Frequently asked questions
Does restoring delete everything on the destination card?
Yes. Write overwrites the entire destination drive, including all partitions and files. Move anything you need off the card first, or use a different card.
Can I restore to a smaller card than the original?
No, not reliably. The destination must be at least as large as the original card, and cards sold as the same size can differ by a few megabytes, so use the same size or larger.
Do I need to decompress a .7z backup before restoring?
Yes. Decompress it back to a plain .img file with 7-Zip first, then write that file with Win32 Disk Imager, which cannot write directly from a compressed archive.
For the full set of guides, see the Tutorials hub, and get the program from the download page. Related guides include: how to back up sd card to img, compress img file 7zip, clone one sd card to many — each one covers one job in the same plain style as this guide.