Problem scenario
You have a Windows laptop with a DVD player. You want to boot to a Linux hard drive from time-to-time. But you do not want to dual boot the same hard drive (where one hard drive supports two different bootable OSes). What should you do?
Solution
You should purchase a hard drive adapter (aka a caddy) made to interface with the internal DVD player connection. You will lose space for your DVD player if you do this (and have one fewer DVD drives). But if you have a second hard drive, it can go where the DVD player is. (If you change your mind later and want to go back to having a DVD player, you can do that.)