On the second part, Macs boot with UEFI, and the boot process is configured via a small number of variables stored in writable firmware memory [1]. Apple provid

On the second part, Macs boot with UEFI, and the boot process is configured via a small number of variables stored in writable firmware memory [1]. Apple provides a command-line tool, nvram(8) [2], which can either print the current contents of the variables (nvram -p), or request a change to one. Changes are queued and written out at the next clean shutdown or reboot. [1] A brief description: https://en.wikipedia.org/wiki/Unified_Extensible_Firmware_Interface#Booting https://en.wikipedia.org/wiki/Unified_Extensible_Firmware_In... [2] https://developer.apple.com/library/mac/documentation/Darwin/Reference/ManPages/man8/nvram.8.html https://developer.apple.com/library/mac/documentation/Darwin...