What Is a Disk Image?A disk image is a compressed file of a bit-by-bit, sector-by-sector copy of a computer hard drive’s contents or other storage media. In this context, it is a compressed file containing a copy of the contents in your SD card. This bit-by-bit file copying is ideal for backups because it creates an identical, bit-by-bit clone that you can restore later.
An SD card being inserted into a computer
How To Create an Image File From SD Card in WindowsIn Windows, you can use the Win32 Disk Imager or DD-for-Windows utility tool. You will also need a PC with a card reader or an SD card-to-USB adapter to connect to your PC.
Using Win32 Disk ImagerBegin by connecting the SD card you want to clone to your computer using its built-in card reader or a Micro SD card-to-USB adapter. Download the Win32 Disk Imager tool, then install and run the application. Click the drop-down arrow under “Device” in the pop-up window to pick the drive letter. Check under “My Computer” to see which letter your SD card has taken. After that, click the folder icon immediately left of the letter you selected. Pick a location in your computer for storing the image file, and give it a name. This file should have a .img extension. Click the “Read” button to begin the cloning process. Give your PC some time and don’t shut it off, close the lid, or put it to sleep. When the process is complete, a window will appear to show successful reading. You can now delete the contents in your SD card and use it to store other things.
Image File Restoration Using Win32 Disk ImagerInsert the SD card into your computer and open the Win32 Disk Imager tool. Select the drive letter in the device drop-down section, then click the folder icon to access the file from where you saved it. Instead of clicking “read,” click “write” and give your PC time to complete the restoration process. The tool will save the image in your memory card, making it appear as when you created the backup file. Generally, the image creation and restoration process length depends on the SD card size. It is vital to note that the image creation or backup matches the SD card size, not the contents stored in the card. For instance, if the SD card capacity is 32GB, the image file will be 32GB even if the data inside only occupies 1 GB. Remember, a disk image is a bit-by-bit copy. So it clones the data and sectors in the storage media.
A 32GB SD cardSo creating a disk image for a 32GB SD card and restoring it takes more time than doing the same for an 8GB card, even if the amount of data inside is the same. And the former will occupy more space in your hard drive.
DD for WindowsWindows operating systems lack the DD command line utility. But it is ubiquitous in Linux and Unix systems. However, you can download DD for Windows externally. After downloading, unzip the file and note its file location. Next, connect the SD card to your PC and note its disk number. It should be disk one if you don’t have other removable storage devices plugged into your computer. After that, open the command line and run it as an administrator. You can hit the windows button, then type “cmd.” Right-click the command line result from the search and select run as administrator. In the cmd window, change the directory using the cd command to the directory where you extracted the DD utility tool. Next, enter type this line, then hit enter to clone the SD card contents into an image file. The DD command takes three parameters to do the cloning.
- IF: input file, which is the SD card (we assume the disk number is 1)
- OF: output file, which states the storage location and file name of the image
- BS: block size, which is one megabyte