What is the ROM identifier?

The Rabbit 3000 and 6000 (but no other Rabbits), according to the user manuals, have a Global ROM Configuration Register (GROM). Unfortunately, the user manual doesn’t really discuss them. In particular, there is a 4-bit “ROM identifier for this version of the chip” part.

What is this ROM identifier?

I’m not sure. I’m not seeing much in the documentation about it (or GRAM), and Dynamic C 9 and 10 don’t make use of it other than having the Pilot BIOS report it.