The non-maskable interrupt (NMI) is the only interrupt which is not
disabled by the CLI instruction, so it can be used in special cases that
need immediate attention.

It is designed to handle catastrophic problems such as a power failure.
In a fail-safe system, the NMI could dump RAM to disk storage in an
attempt to save data before all was lost.

In the standard PC BIOS, the NMI is hard-wired to be executed in the event
of a memory parity error.  When it occurs, the PC locks up and dies.  Now
don't you feel safer knowing that everything in memory will be lost rather
than a few bits?

The 8087/80287 math coprocessor is tied to the NMI line and causes an
interrupt when it encounters an exception condition (e.g., division by 0).

Typically you must read I/O Port 64H to find if a memory error occurred
and if not, perform an FNSAVE to find what caused the 8087 exception, then
FNCLX to clear the error.

Note: PCjr uses the NMI to detect keystrokes from the infrared linkup.

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INT 02H: Non-Maskable Interrupt