Weird Windows 10 Occurrence Open Programs from Previous Installation

[J Zimm]

A few weeks ago I did a format/clean install of windows onto my SSD. The old installation had many programs installed onto a secondary HDD. Today I discovered I can actually launch programs from my secondary HDD that I haven't installed in the new windows installation. This was not an upgrade install because the only drive connected in the computer during the upgrade was the SSD.
What is happening??

 

[gardenman]

Hi, some programs will actually let you run them, even if they haven't been installed on a new copy of Windows. Definitely not all will run. If a program needs to access certain registry entries that was available on the old system, but isn't available on your new system, then the program will likely crash or throw an error and not work.

The same goes for any system files that were installed in your old Windows folder. If a program needs one of those and can't find it in your new systems Windows folder, then it will likely crash or throw an error.

If you find a few good programs that do still work, you might be able to simply copy the whole folder from the old drive to the new drive and get them working correctly. Or just leave them were they are, and create new shortcuts to them in your Start Menu and desktop. Like I said, not all programs will allow this.

 

[USAFRet]

A few weeks ago I did a format/clean install of windows onto my SSD. The old installation had many programs installed onto a secondary HDD. Today I discovered I can actually launch programs from my secondary HDD that I haven't installed in the new windows installation. This was not an upgrade install because the only drive connected in the computer during the upgrade was the SSD.
What is happening??

Some do, some don't.
Some do, but lose any settings (in the old Registry).

Far easier to assume 'don't' for all, and then reinstall all of them.
Rather than trying to determine "this one yes, that one no".