Jargon File “A comprehensive compendium of hacker slang that illuminates many aspects of hacker tradition, folklore, and humor.” The first version was compiled by a computer scientist named Raphael Finke at Stanford in 1975. It has been maintained by various people over the years and hosted on various computers, but in recent years the canonical version has been edited by Eric Raymond (author of the influential article, “Cathedral and Bazaar“).
A few years ago, I (GLS) was wandering around the cabinets housing the MIT AI Lab’s PDP-10 and noticed a small button affixed to the frame of a cabinet. It was obviously a homebrew job (no one knows who) added by one of the lab’s hardware hackers.
You wouldn’t touch an unknown key on the computer without knowing what it was doing because you could crash the computer. The key has been tagged in the most useless way. It had two positions, and the words ‘magic’ and ‘more magic’ were scribbled in pencil on the metal key body. The switch was in the ‘more magical’ position.
I summoned another hacker to take a look. He had never seen the key before, either. Closer inspection revealed that the switch had only one wire going to it! The other end of the cable is lost in a 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 the other.
It was clear that this key was someone’s stupid joke idea. We turned it because we believed the key was not working. The computer suddenly crashed.
Think of our great surprise. We wrote this as a coincidence, but still set the switch back to the ‘more magic’ position before reviving the computer.
A year later, I told this story as I remember it to another hacker, David Moon. He clearly doubted my sanity, or suspected that I had a supernatural belief in the power of this key, or perhaps thought I was deceiving him with a false myth. To prove it to him, I showed him the key, which was still in the ‘more magic’ position and was glued to the cabinet frame with only one wire attached. We examined the switch and its only connection and found that the other end of the cable is connected to a ground pin, although it is connected to the computer wires. This clearly rendered the switch doubly useless: not only was it electrically powered, it was also connected to something that could not affect anything. So we turned the key.
The computer suddenly crashed.
This time, we ran for Richard Greenblatt, a longtime MIT hacker who was nearby. He hadn’t noticed the key before, either. He examined it, concluded it was useless, took some cross cutters and steep outside. We then revived the computer and it has been working fine ever since.
We still don’t know how the key broke the machine. There is a theory that some circuits near the ground pin are marginal and that turning the switch changes the electrical capacitance enough to overturn the circuit as pulses pass through in a millionth of a second. But we will never know for sure; all we can really say is that the key spell.
I still have that key in my basement. Maybe I’m stupid, but I usually set it to ‘more magic’.
1994: Another explanation of this story has since been offered. Note that the key body is metal. Suppose the unconnected side of the switch is connected to the switch body (usually the stem is connected to a separate ground lug, but there are exceptions). The body is connected to the computer case, which is probably grounded. Now, the circuit ground inside the machine is not necessarily at the same potential as the chassis ground, so flipping the switch will connect the circuit ground to the chassis ground, causing a voltage drop/jump that resets the machine. This was probably discovered by someone who found out the hard way that there was a potential difference between the two and then jokingly wired the switch.
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