I have a 1 TB Western digital 3.5 inch hard drive that I pulled out of a Mac Pro computer. It was the main boot drive and i think it had OS X Yosemite on it. Since I replaced this with an SSD boot drive, I have no longer needed the Western digital drive. I thought of erasing it in disk utility and making it a fresh blank drive to sell on eBay, but then I thought should I leave the OS X Yosemite on it? and sell it as a boot drive? and if I wanted that OS, could I copy it onto a thumb drive to install on another mac? before I sell it?