[1] : Jargon File (4.3.1, 29 Jun 2001)

a story about `magic'

some years ago, i gls 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 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.

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'.

1994: another explanation of this story has since been offered. note that
the switch body was metal. suppose that the non-connected side of the
switch was connected to the switch body usually the body is connected to a
separate earth lug, but there are exceptions. the body is connected to the
computer case, which is, presumably, grounded. now the circuit ground
within the machine isn't necessarily at the same potential as the case
ground, so flipping the switch connected the circuit ground to the case
ground, causing a voltage drop/jump which reset the machine. this was
probably discovered by someone who found out the hard way that there was a
potential difference between the two, and who then wired in the switch as a
joke.


see also:
dike magic 

About >> A Words
About, definition of term: About
about_pag1.html

Magic >> M Words
Magic, definition of term: Magic
magic_pag1.html

Magic Cookie >> M Words
Magic Cookie, definition of term: Magic Cookie
magic+cookie_pag1.html

Magic Wand >> M Words
Magic Wand, definition of term: Magic Wand
magic+wand_pag1.html

Magic Realism >> M Words
Magic Realism, definition of term: Magic Realism
magic+realism_pag1.html

Go About >> G Words
Go About, definition of term: Go About
go+about_pag1.html

Life Story >> L Words
Life Story, definition of term: Life Story
life+story_pag1.html

Get About >> G Words
Get About, definition of term: Get About
get+about_pag1.html

Deep Magic >> D Words
Deep Magic, definition of term: Deep Magic
deep+magic_pag1.html

Be About >> B Words
Be About, definition of term: Be About
be+about_pag1.html

Page 1 2 3 4 Next