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 for Magic Switch Story
From The Free On-line Dictionary of Computing (30 December 2018) :

  Magic Switch Story
  
     Some years ago, I was snooping around in the cabinets that
     housed the MIT AI Lab's PDP-10, and noticed a little
     switch glued to the frame of one cabinet.  It was obviously a
     homebrew job, added by one of the lab's hardware hackers
     (no-one knows who).
  
     You don't touch an unknown switch on a computer without
     knowing what it does, because you might crash the computer.
     The switch was labelled in a most unhelpful way.  It had two
     positions, and scrawled in pencil on the metal switch body
     were the words "magic" and "more magic".  The switch was in
     the "more magic" position.
  
     I called another hacker over to look at it.  He had never seen
     the switch before either.  Closer examination revealed that
     the switch had only one wire running to it!  The other end of
     the wire did disappear into the maze of wires inside the
     computer, but it's a basic fact of electricity that a switch
     can't do anything unless there are two wires connected to it.
     This switch had a wire connected on one side and no wire on
     its other side.
  
     It was clear that this switch was someone's idea of a silly
     joke.  Convinced by our reasoning that the switch was
     inoperative, we flipped it.  The computer instantly crashed.
  
     Imagine our utter astonishment.  We wrote it off as
     coincidence, but nevertheless restored the switch to the "more
     magic" position before reviving the computer.
  
     A year later, I told this story to yet another hacker, David
     Moon as I recall.  He clearly doubted my sanity, or suspected
     me of a supernatural belief in the power of this switch, or
     perhaps thought I was fooling him with a bogus saga.  To prove
     it to him, I showed him the very switch, still glued to the
     cabinet frame with only one wire connected to it, still in the
     "more magic" position.  We scrutinized the switch and its lone
     connection, and found that the other end of the wire, though
     connected to the computer wiring, was connected to a ground
     pin.  That clearly made the switch doubly useless: not only
     was it electrically nonoperative, but it was connected to a
     place that couldn't affect anything anyway.  So we flipped the
     switch.
  
     The computer promptly crashed.
  
     This time we ran for Richard Greenblatt, a long-time MIT
     hacker, who was close at hand.  He had never noticed the
     switch before, either.  He inspected it, concluded it was
     useless, got some diagonal cutters and diked it out.  We
     then revived the computer and it has run fine ever since.
  
     We still don't know how the switch crashed the machine.  There
     is a theory that some circuit near the ground pin was
     marginal, and flipping the switch changed the electrical
     capacitance enough to upset the circuit as
     millionth-of-a-second pulses went through it.  But we'll never
     know for sure; all we can really say is that the switch was
     magic.
  
     I still have that switch in my basement.  Maybe I'm silly, but
     I usually keep it set on "more magic".
  
     GLS
  
     (1995-02-22)
  

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