HDD formatting question?

Hi,

I want to get a new hdd for my primary drive which is easy enough will probs throw the current primary drive away, i have a 2nd 500gb hdd that i use to store all my stuff on video's, game's & music etc and some of the games are installed on the "B" drive which is the 500gb one

MY QUESTION - if i install the operating system on the new hdd that i will get will i have to format my 2nd drive and re-install everything on that?

My guess is that i don’t and should work just like plugging an external hdd in but would like to know 100%.

I’m not a novice when it comes to computers but was just wondering as never been in this situation before

Thanks in advance

Peace Tim