SIGIOT and SIGEMT - and floating point on a PDP11

[R McBurnett]

The EMT instruction on a PDP-11 computer is an emulate trap instruction
intended to emulate a real hardware interrupt.  At a guess it's original
purpose was to let software types tryout new software before the hardware was
ready.  THEN someone had a good idea about how to use it ?intelligently? in
an operating system.. Both RSX11-M and RT11 used it extensively.

BTW the TRAP instruction works the same way as EMT but to a different vector,
and is useful for user programs that want to test hardware interrupts.

Roe McBurnett		{ihnp4!packard,topaz}!nvuxr!rdm2
Bell Communications Research, Red Bank NJ