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)
In addition suitable contents:
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