I have an iMac running OS X Yosemite 10.10.5, with iTunes 12.3. I want to transfer my music to an external hard drive, but here is the difference:
I don't want to transfer it to another computer. I want all my music on my iMac referenced on my iMac, but located in my external hard drive. That means, if I eject my drive, I can't hear the music because it's not on my iMac. I would still want the possibility to see my list of songs in the iTunes program.