Sometimes it would be great to be able to try different versions of the OS X operating system before upgrading. This is easy if you have a number of Macs, less so if you have just one. In this tutorial I’ll show you how to install OS X on an external drive without replacing the particular version of the operating system, on the Mac, itself.
Whilst this tutorial is entitled How to Install OS X Yosemite Onto an External Volume, the same principles apply for installing Lion, Mountain Lion or Mavericks on to an external volume.