GLOSSARY
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API (Application Program[ming] Interface)
   An API is the set of function calls and services that a
   program makes available to other processes (applications).
   Each function or service has a set format which specifies
   the values to be supplied by the caller and the values
   which are returned.  Because of this interface
   specification, the underlying organization of the
   function or service can be changed without affecting the
   applications which use it.  For example, the DOS INT 21h
   file access functions remained unchanged between DOS 2.x
   and DOS 3.x, even though the internal data structures and
   code organization changed significantly.

NMI (Non-Maskable Interrupt)
   Most external (hardware) interrupts can be disabled by the
   CLI (CLear Interrupt enable flag) instruction when the CPU
   is executing critical code that should not be interrupted,
   such as switching from one stack to another.  However, there
   are some situations so dire that the CPU must act on them
   immediately no matter what else it is doing, even if it has
   disabled interrupts.  The Non-Maskable Interrupt serves
   precisely this purpose, as it cannot be disabled (masked) by
   the CPU.
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