Next, you will need enough disk space available, for example, to create Recovery Partition. Note, that it is recommended that you install OS on a clean drive. The chart below tells you how much free space is needed. One more argument is that the free space on your disk translates into virtual memory so your apps have “fuel” to operate on.

This includes not just space for the OS itself but also space for other applications and your user data. Given your Mac isn’t new and is filled with data, you will probably need enough free space on your Mac. We’ll be repeatedly referring to these Apple OS versions below, so it’s good to know the basic macOS timeline. Further down we’ll explain where to get one and what problems you may face down the road. 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.

It removes only safe-to-delete files and is notarized by Apple. So here’s the tip for you: download CleanMyMac X to refresh your Mac’s drive automatically.

Install os x el capitan mac air