An integrated circuit chip installed in the onboard computer which has been programmed with operating instructions and database information for a particular vehicle.

ROM chip on which items, called microcode, can be placed permanently; once a programmer writes the microcode onto the chip, it functions like a regular ROM chip and cannot be erased or changed. 4.20

A programmable read-only memory (PROM) or field programmable read-only memory (FPROM) is a form of digital memory where the setting of each bit is locked by a fuse or antifuse. Such PROMs are used to store programs permanently. The key difference from a strict ROM is that the programming is applied after the device is constructed.