NMI (Non-Maskable Interrupt)

A server is always executing interrupts; giving attention to whatever needs it. These are so-called maskable interrupts. The CPU can mask, or temporarily ignore, any interrupt if it needs to in order to finish something else that it is doing. There are also non-maskable interrupts (NMI), which are used for serious conditions that demand the processor’s immediate attention.

When an NMI signal is received, the processor immediately drops whatever it was doing and attends to it. The NMI cannot be ignored by the server. The NMI signal is normally used for critical problem situations, such as serious hardware errors. The most common use of NMI is to signal a parity error from the memory subsystem.