I particularly liked the part about EPROMs and PROMs.
Firmware can include:
Jump tables relating to hardware.
Model and revision numbers.
Serial Numbers
Coded Trade Secrets
Data required for specific actions
Secret data having nothing to do with the operation of the equipment that is placed there for product marking for copyright protection.
Software that instructs hardware to do specific actions
Anything else the firm that creates the hardware and firmware wants.
It can be hard-coded into a piece of hardware... as was the case of the ROM, not PROM, or EPROM, or EEPROM, installed on the original IBM-PCs, which IBM burned at their chip foundry. It became a piece of hardware, a black box, so to speak, which took input and provided specific output for certain input. Compaq hired a team of 18 engineers, some of whom did indeed take a BIOS ROM from a working IBM-PC and map the inputs provided by an IBM-PC and make a second related map of the output sent to the IBM-PC. This chart of input = output was then handed to a team who had not touched the BIOS ROM who then REVERSE ENGINEERED a set of instructions that duplicated the output with the given input. They then burned that data to their own piece of hardware, a COMPAQ BIOS ROM.
Some companies, attempting to build computers that operated exactly like an IBM-PC, merely cloned the IBM-PC BIOS ROM... and were rightly sued for copyright infringement and appropriation and conversion of IBM trade secrets. IBM tried to aggressively protect its market with its only protect-able item... the BIOS ROM.
This black box, this piece of hardware, was the only IBM created TRADE SECRET and PROPRIETARY item included in their IBM-PC. The legal reverse engineering of the contents of this piece of hardware resulted in IBM's control of the PC hardware being abrogated.
Kudos to the folks at Phoenix who did about (or exactly?) the same thing and began selling just the BIOS for about twenty bucks to all takers.
I particularly liked the part about EPROMs and PROMs.