NMI

NMI /N-M-I/ n.  Non-Maskable Interrupt.  An IRQ 7 on the
   PDP-11 or 680[01234]0; the NMI line on an 80[1234]86.  In contrast
   with a {priority interrupt} (which might be ignored, although
   that is unlikely), an NMI is *never* ignored.  Except, that
   is, on {clone} boxes, where NMI is often ignored on the
   motherboard because flaky hardware can generate many spurious
   ones.