Fortunately OS X isn't as bad as Windows. I haven't tried the most recent version, but for previous versions I have successfully installed OS X from a USB stick

Fortunately OS X isn't as bad as Windows. I haven't tried the most recent version, but for previous versions I have successfully installed OS X from a USB stick, without needing any internet access at all. However, the OS X binaries are signed. So, when the key expires, people are SOL. I had this problem, and easily re-downloaded my various older OS X versions. But in the general case it's quite disturbing: http://www.macrumors.com/2016/03/03/older-os-x-installers-broken-by-certificate/ http://www.macrumors.com/2016/03/03/older-os-x-installers-br...