Finally, if you want to run a parallel copy of Mac OS X on a virtual machine, you too will need a working installation file of an older Mac OS X. Also, you may have noticed your Mac's performance went down right after the last update.

To begin with, some of your apps may not be working properly (or simply crash) on newer operating systems. There are many reasons that could point you to this radical decision. So, you've decided to download an older version of Mac OS X. Within OS X Utilities, choose Reinstall OS X. Prepare a clean external drive (at least 10 GB of storage). The following method allows you to download Mac OS X Lion, Mountain Lion, and Mavericks. The Mac OS Mavericks picked up the trust of the end-clients with the expansion of Siri and Apple pay support in safari.