A black box is any device whose workings are not understood by or accessible to its user. According to Edward Tenner, writing in The Washington Post, the first black box was a gun sight carried on World War II Flying Fortresses, with hidden components that corrected for environmental variables, such as wind speed. The crew probably didn't know how the device worked, but they knew it might be crucial to their survival. Nowadays, there are two types of black box carried on aircraft, which may be combined into a single device: a flight data recorder (FDR), which logs information such as speed and altitude, and a cockpit voice recorder (CVR), which logs all voice communication in the cockpit. These black boxes also carry beacons to help find the aircraft in a rescue situation.
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A sampling of other black boxes:
- In telecommunications, a black box is a resistor connected to a phone line that makes it impossible for the telephone company's equipment to detect when a call has been answered.
- In data mining, a black box is an algorithm or a technology that doesn't provide an explanation of how it works.
- In software development, a black box is a testing method in which the tester has no knowledge of the inner workings of the program being tested. The tester might know what is input and what the expected outcome is, but not how the results are achieved. A black box component is a compiled program that is protected from alteration by ensuring that a programmer can only access it through an exposed interface.
- In film-making, a black box is a dedicated hardware device: equipment that is specifically used for a particular function.
- In the theatre and television, a black box is an unfurnished studio.
- In the financial world, a black box is a computerized trading system that does not make its rules easily available.
Perhaps because the metaphor is broadly applicable, black box is sometimes used to refer to anything that works without its inner workings being understood or accessible for understanding.