So basically I am trying to add a second hard drive to my PC. The problem is that it is an old used hard drive from my friend and even he does not know what is on it, but he is pretty sure he used it as the main hard drive for a PC once. My question is, if I were to install this hard drive to my PC along with my main hard drive with windows 8.1 on it, would something catastrophically bad happen If there is an os on my friend's hard drive? If so, would it be possible to format the hard drive and leave my main hard drive alone before booting by booting into a USB windows 8 recovery drive and formatting it there?