software interrupt

   An interrupt caused by a specific machine language
   operation code (e.g. the Motorola 68000's TRAP, the IBM
   System/390's SVC or the ARM's SWI) rather than by a
   hardware event.

   As with a hardware interrupt, this causes the processor to
   store the current state, store identifying information about
   the particular interrupt, and pass control to a first level
   interrupt handler.

   A trap is similar except that it is caused by an unexpected
   software condition or error (e.g. divide by zero, undefined
   instruction) rather than a deliberate instruction.

   (1995-02-14)