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In electronics, "magic smoke" is the stuff that lets components work: once the magic smoke leaves the component, the component ceases to work.

What is the earliest reference in print to "magic smoke"? Internet posts don't count. The Jargon File v2.8.1 (1991) mentions Jay Maynard referencing magic smoke, so I'm looking for print references prior to 1991.

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  • My guestimate of when I first heard the expression would be about 1985.
    – Hot Licks
    May 8, 2016 at 1:27
  • The joke was along the lines of: Did you know that computers run on smoke? They stop working when the smoke gets out. (The idiom "smoke test" goes back much further -- I'm sure I heard it and used it in the 70s.)
    – Hot Licks
    May 8, 2016 at 1:30
  • Are you asking about the phrase, or the phrase with reference to electronic components?
    – JEL
    May 8, 2016 at 3:19
  • The phrase with reference to electronic components.
    – Robert B
    May 8, 2016 at 18:24
  • I can't provide any references, but the basic concept certainly dates back to at least the mid-1970s. When powering up new electronic circuits one of my colleagues (ex Royal Navy) routinely said "Switch to custard and tune for minimum smoke". I didn't encounter the concept of magic smoke until some time in the 1980s. Jul 30, 2022 at 16:11

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An entry for "magic smoke" in the context of computers appears at least as early as 1990. From The Jargon File, Version 2.1.1 (Draft) (June 12, 1990):

MAGIC SMOKE (ma'jik smohk) n. A notional substance trapped inside IC packages that enables them to function. Its existence is demonstrated by what happens when a chip burns up -- the magic smoke gets let out, so it doesn't work any more. See SMOKE TEST.

No such term appears in the original jargon.txt file, from circa 1983 and earlier, however. The closest entry it offers is simply for "smoke," which is a much more general term and only tangentially—if at all—related to "magic smoke":

MAGIC adj. 1. As yet unexplained, or too complicated to explain. (Arthur C. Clarke once said that magic was as-yet-not-understood science.) "TTY echoing is controlled by a large number of magic bits." "This routine magically computes the parity of an eight-bit byte in three instructions." 2. (Stanford) A feature not generally publicized which allows something otherwise impossible, or a feature formerly in that category but now unveiled. Example: The keyboard commands which override the screen-hiding features.

Eric Raymond, The New Hacker's Dictionary, third edition (1996) elaborates on the 1990 entry as follows:

magic smoke n. A substance trapped inside IC packages that enables them to function (also called blue smoke; this is similar to the archaic 'phlogiston' hypothesis about combustion). Its existence is demonstrated by what happens when a chip burns up — the magic smoke gets let out, so it doesn't work any more. See smoke test, let the smoke out.

Usenetter Jay Maynard tells the following story: "Once, while hacking on a dedicated Z80 system, I was testing code by blowing EPROMs and plugging them in the system, then seeing what happened. One time, I plugged one in backwards. I only discovered that after I realized that Intel didn't put power-on lights under the quartz windows on the tops of their EPROMs -- the die was glowing white-hot. Amazingly, the EPROM worked fine after I erased it, filled it full of zeros, then erased it again. For all I know, it's still in service. Of course, this is because the magic smoke didn't get let out." Compare the original phrasing of Murphy's Law.

One instance of "magic smoke" in the wild from before 1990—from the field of audio electronics, not computing—seems relevant. From an unidentified article about amplifier kits in The Absolute Sound, volume 14, issues 58–59 (April/May–June 1989) [combined snippets]:

Taking off the bottom cover on a kit-built component is a moment akin to pulling that RCA or Mercury out of its jacket in a musty old record store. Will it be good? Kit-built components up the ante and crank up the degree of difficulty in evaluating equipment. Following the trinity of commandments of collecting: condition, condition, and again condition, becomes even more challenging. Some people feel this level of difficulty is what makes owning old components so much fun. With kits, it's always possible that you will luck upon the works of an electronic Leonardo. Kits are magic boxes, capable of revealing pearls or just plain letting the smoke out.2

2 "Letting the smoke out" is such a wonderful phrase, coined by some witty engineer to describe the phenomenon of an amplifier going up in smoke. The basic concept here is that all electronic devices are magic boxes run on supernatural smoke. When they break, all that really happens is the cabinet springs a leak and lets the magic smoke out. Sounds pretty good to me.

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