Internet Recovery

Since the release of Mac OS X Lion:

  • Holding down Command + R at startup told your Mac to boot from the local Recovery Partition, allowing you to restore your Mac’s installed operating system.
  • Holding down Command + Option + R at startup told your Mac to NetBoot from Apple’s Internet Recovery, allowing you to restore your Mac to its original operating system.
This all changed on Tuesday when Apple released macOS 10.12.4.

Apple:

macOS Recovery installs different versions of macOS depending on the key combination you press while starting up. Hold down one of these combinations immediately after pressing the power button to turn on your Mac. Release when you see the Apple logo or a spinning globe.
Michael Tsai:
The new Option-Command-R keyboard shortcut lets you do an Internet recovery of latest macOS that is compatible with your Mac. So, rather than boot from a slow hard drive, wrangle the Mac App Store, download the installer, and then launch it, I just held down the keys and let it download and install all at once. The time estimate was way off (under), but other than that it worked smoothly and got my Mac booting again.
Internet Recovery is now a convenient time-saver, skipping the unpatched versions of system software and restoring the latest Mac OS. I am a fan just as long restoring older versions of Mac OS are still an option. One of my least favorite aspects of iOS is that you cannot install the version of system software that originally shipped with your device.