Magic smoke is smoke produced by malfunctioning electronic circuits. The origins of the magic smoke have become a running

Running gag

A running gag, or running joke, is a literary device that takes the form of an amusing joke or a comical reference and appears repeatedly throughout a work of literature or other form of storytelling....

 in-joke

In-joke

An in-joke, also known as an inside joke or in joke, is a joke whose humour is clear only to people who are in a particular social group, occupation, or other community of common understanding...

 that started among electrical engineers

Electrical engineering

Electrical engineering is a field of engineering that generally deals with the study and application of electricity, electronics and electromagnetism. The field first became an identifiable occupation in the late nineteenth century after commercialization of the electric telegraph and electrical...

 and technician

Technician

A technician is a worker in a field of technology who is proficient in the relevant skills and techniques, with a relatively practical understanding of the theoretical principles. Experienced technicians in a specific tool domain typically have intermediate understanding of theory and expert...

s before it was more recently adopted by computer programmers. The actual origin of blue smoke is the black plastic epoxy material that is used to package most common semiconductor devices such as transistor

Transistor

A transistor is a semiconductor device used to amplify and switch electronic signals and power. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current...

s and integrated circuit

Integrated circuit

An integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...

s, which produces a bluish coloured smoke during combustion

Combustion

Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame...

. Smoke from other components that do not use this epoxy may vary in colour, but still be identified as the same phenomenon for purposes of the joke.

Joke

Smoke is frequently observed to come out of electronic

Electronics

Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...

 components when overheated, often through exposure to an extreme electrical current usually caused by a low-resistance failure or the application of excess voltage

Voltage

Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...

 through some cascading failure of the circuit. According to the joke, manufacturers put a portion of magic

Magic (paranormal)

Magic is the claimed art of manipulating aspects of reality either by supernatural means or through knowledge of occult laws unknown to science. It is in contrast to science, in that science does not accept anything not subject to either direct or indirect observation, and subject to logical...

 smoke into every electronic component, and the device functions normally so long as the smoke does not escape. Once the magic smoke has been released, the device lacks one or more key components and no longer functions correctly. The smoke thus can be thought of as an essential part in the device's function. It is also noted that once let out, the magic smoke cannot be put back in. The joke deliberately uses common logical fallacies to humorously characterize the causes and effects of electronic device failure.

Power plants produce the smoke and send it to their customers through a grid of power lines. If they produce more smoke than the customers can use, the excess smoke goes out the stack.

In some variations of the joke, it is alleged that the major microchip production companies (especially the large microprocessor

Microprocessor

A microprocessor incorporates the functions of a computer's central processing unit on a single integrated circuit, or at most a few integrated circuits. It is a multipurpose, programmable device that accepts digital data as input, processes it according to instructions stored in its memory, and...

 manufacturers) are involved in a conspiracy

Conspiracy theory

A conspiracy theory explains an event as being the result of an alleged plot by a covert group or organization or, more broadly, the idea that important political, social or economic events are the products of secret plots that are largely unknown to the general public.-Usage:The term "conspiracy...

 to keep the true nature of their products under wraps.

Usage

This has led to use of the phrases (and variants of) "leaking smoke", "the magic smoke is escaping", or "you let the smoke out!" as a euphemism

Euphemism

A euphemism is the substitution of a mild, inoffensive, relatively uncontroversial phrase for another more frank expression that might offend or otherwise suggest something unpleasant to the audience...

 for the destruction of a processor, integrated circuit

Integrated circuit

An integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...

 or other electronic component, by overheating.

When a device is powered on for the first time, it is often called a "smoke test".

External links

• Magic smoke entry in the Jargon File
  Jargon File
  The Jargon File is a glossary of computer programmer slang. The original Jargon File was a collection of terms from technical cultures such as the MIT AI Lab, the Stanford AI Lab and others of the old ARPANET AI/LISP/PDP-10 communities, including Bolt, Beranek and Newman, Carnegie Mellon...
  
  
• Magic smoke entry at FOLDOC
• Lucas Replacement Wiring Harness Smoke (for automotive electrics)
• "Magic Blue Smoke Refilling Kit" Magic Smoke Refill kit from Sparkfun