[2456] in Depressing_Thoughts
Re: no more magic
jik@ATHENA.MIT.EDU (jik@ATHENA.MIT.EDU)
Tue Oct 22 14:38:25 1991
It's in the book, I believe, but not under the definition of "magic".
See in Appendix A, under the heading, "Two Stories About `Magic' (by
GLS)".
And, for the edification of those who are now curious, here's the
whole story:
Two Stories About `Magic' (by GLS)
==================================
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 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
{dike}d 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'.
