Building a new PC. Can I use the OS on my hard drive on my new PC?

[Yuki Haske]

I currently have an All-in-one with a 1tb hard drive. I am looking to build a pc to start gaming, but I do not want to have to buy a new hard drive. Can I just take my old hard drive out and plug it into my new PC? I have an Windows 8.1 and all my files on it. Or would I have to buy windows 8 again install it on a new hard drive then transfer my files over?

 

[popatim]

Its my understanding that windows 8 OEM is fully transferable to your new computer.
http://www.microsoft.com/oem/en/licensing/sblicensing/Pages/windows-licensing-for-personal-use.aspx#fbid=rK8velXCIRT