The prom(1) reference page, accessible with the command:
contains valuable information about the PROM monitor on your system.man prom
PROM stands for Programmable Read-Only Memory. Most PROM chips are placed in your computer at the factory with software programmed into them that allows the CPU to boot and allows you to perform system administration and software installations. The PROMs are not part of your disk or your operating system; they are the lowest level of access available for your system. You cannot erase them or bypass them.
Since PROMs are not normally changed after the manufacture of the system, newly added features will not be present on older systems. Some systems have PROM firmware that responds to new programming when the operating system is updated. See your hardware Owner's Guide for more information on these types of PROMs.
Note that there are numerous minor differences between machines, and you should refer to your Owner's Guide and Release Notes for information specific to your machine.
Newer systems use a PROM called the ARCS prom. ARCS stands for Advanced Risc Computing Standard. This PROM provides a graphical interface and allows the use of the mouse to control booting and execution. ARCS systems allow the use of the keyboard, and the older key syntaxes have been retained for compatibility. Systems that use the ARCS prom include the Indigo R4K, Indy, Indigo2, CHALLENGE, Onyx, some Crimson systems, and others.
This chapter contains information on the following topics: