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Once a VM snapshot is made within VirtualBox, you turn the VM off and delete the ISO, knowing that it no longer serves a purpose and you want to save disk space.
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Meanwhile, it would seem prudent for you to create a snapshot of your virtual machine (VM) in the exact state it is in, in case something should go wrong. After setting up the virtual machine, you get the guest operating system booted up and you mount an ISO image to the virtual disc drive for further examination. So you just finished an operating system install within VirtualBox that you plan to use for testing purposes.
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