Apple TIL on bootROM vs. Mac OS ROM

Apple TIL article #58492 offers a good explanation of the difference between bootROM and Mac OS ROM (two new buzzwords with Apple's latest hardware, starting with the iMac):

The bootROM holds most of the hardware-specific components needed to boot the specific logic board. Low-level hardware-specific code still exists in firmware (ROM) in order to handle the computer's start-up activities. This code fits into one physical ROM chip called the bootROM.

The Mac OS ROM image file, present in the system folder, contains boot-time Mac OS routines and hardware-specific software components that are common to many Macintosh computers.