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		From "The Hacker's Dictionary", Guy Steele et. al.

Some years ago I was snooping around in the cabinets that housed the MIT AI
lab's PDP-10, and I 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).  The switch was labeled 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.  Closer examination revealed that the switch only had 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.  Convinced by
our reasoning that the switch was inoperative, we flipped it.  The computer
instantly crashed!  A year later, I told this story to yet another hacker.
He clearly doubted my sanity.  To prove it to him, I showed him the very
switch, still glued to the cabinet frame with only one wire connected to it.
It was 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 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.

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."

		- Guy Steele, "The Hacker's Dictionary"

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