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Reading an old .pqi file (solution)
I finally solved the issue described in this thread: https://community.norton.com/en/node/1488041
The thread has been closed and I can't post my solution there, so I'm putting it here in the hope that some poor soul who's in the same position might find it.
To re-cap the problem: I had an old .pqi file which (as it turned out) contained a drive image created with the PowerQuest Drive Image software in the Windows 95 era. Symantec Ghost, which apparently is supposed to be able to read .pqi files, was unable to.
After long searching, I was able to use this publicly available version of PowerQuest Drive Image 2002 to read the file. Since it is MS-DOS based, I had to download the ISO file and boot a Virtualbox VM with it, but from there I was able to restore the drive image to a drive of the VM (which can then be mounted and read by the host OS).
A somewhat involved procedure, but the only way I was able to get to my files. Hope this helps someone!