Battery signal on the HP 95LX.

In the original IBM PC, an NMI was triggered if a parity error was detected in system memory, or reported by an external device. In either case, the PC would display an error message and halt. Some later IBM-compatibles used an NMI to conceal the hardware differences from that of the original IBM PC. On such computers, an NMI would be generated when a program attempted to access incompatible