I have 1 hard drive in my pc and the other one from the laptop with win 8 also built into the pc. If I select the laptop hard drive as boot, can I use Win 8 and Win 10? So Win 8 on the laptop HDD and Win 10 on the other?
I don't see any reason why this shouldn't work. You just have to choose the right hard drive in the BIOS to boot. What that brings then is of course the other question.
Thanks. I have GTA V on the second HDD and don't want to install it again, but somehow my PC runs better on Win 8 than Win10, I can't explain it to myself.
Just copy GTA V over ^^ How long have both OS been installed? HDDs and Windows don't really like each other. The longer Windows tinkers with it without being reset, the slower the OS becomes. This can make Windows 8 run better. I therefore recommend backing up your data on an external hard drive and reinstalling Windows about once a year if it is installed on an HDD. That helps a lot. Incidentally, support for Windows 8 has been discontinued, which means that the operating system no longer receives security updates, which makes it easier to attack. Therefore I would refrain from using it, if otherwise possible.