The Jargon File (version 4.4.7, 29 Dec 2003):

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.


The Free On-line Dictionary of Computing (30 December 2018):

magic smoke

    A substance trapped inside integrated
   circuit 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 Electing a Pope, smoke test.

   Usenetter Jay Maynard tells the following story:

   "Once, while hacking on a dedicated Zilog 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
   backward.  I only discovered that *after* I realised 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.

   [Jargon File]

   (1995-01-25)