The .isz file format is a compressed Zip file of an ISO image. ISO is the content of a CD placed onto a hard drive so you can recreate the exact CD. Because these files can take up a large amount of storage space, .isz files are used to reduce the file size. However, the only way you can gain access to the ISO disc image is by extracting the contents back to their original format.
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Locate the .isz file on your computer. Right click the file and choose the "Extraction" option provided. A Zip extraction window appears on the screen.
Set an extraction location for the files to be saved to. Selecting the desktop allows you to easily find the extracted ISO; however, you can save the file to any other location.
Click "Extract" and the .isz file is extracted, leaving you with the ISO file. You are now free to open the ISO file or burn the contents onto a CD.