Ever since the release of Mac OS Lion the software upgrades for Macintosh computers are distributed through the online app store. Be it a clean install or upgrade, mac app store require you connect to the internet to download whole installation files. The online OS update is okay if you have stable broadband connectivity and enough bandwidth. Apple also provides an option for internet recovery of macOS if your computer fails to boot. But there are situations where you can’t download the OS from the Apple servers. Having a bootable macOS offline installation disk is the only solution in such scenarios.