Having an independent bootable USB drive or SD Card also makes sense in case you want to install Mountain Lion on multiple computers without having to download it time and again.

Etcher is the easiet ISO image burning software we've come across in a very long time that allows you to Flash OS images to SD cards & USB drives.

Lion Diskmaker has been updated to allow you to make a bootable USB or SD Card installer on a 8GB piece of media. The process is straightforward: 1.

Etcher can actually make a bootable SD card from any operating system image, but we’ll be using it for Raspberry Pi images more than anything else.

All you'll need is a Mac, the Mojave installer, and an 8GB USB drive or SD card. Read the whole story ...