how do i add old hdd to new computer without the old os coming up?

[lovesthunder]

I bought a new computer with windows 10. and i want to add my drive from my old computer but not the OS (windows 7) that is on it. how can i do that and not lose all my files?

 

[alexoiu]

You'd just connect it to the new system and, when starting the system, entering BIOS and making sure that the drive with Win 10 on it is the primary bootable device.