

| The Black Box |
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| Without logos or identifying marks, a black box can be any device custom made to solve a problem. |
| A Little Black Box |
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| The 10-ounce device lying on top of this CD changer is an Apple TV set-top box. See Apple TV. |
(in Russian, chernyi iashchik), an object of study whose internal structure either is unknown or is too complex for any conclusions about the behavior of the object to be drawn on the basis of the properties of the object’s elements or on the basis of the structure of the connections between the elements. In Russian, the term chernyi iashchik is also used to refer to the method of studying such objects.
The black-box method is used in cases where an outside observer knows only the input to an object and the object’s response; in such cases, the processes occurring within the object are unknown. The study of a multiterminal network whose internal circuitry is unknown provides a very simple example of the use of the black-box method. By observing the behavior of such an object for a sufficiently long time and, if necessary, by carrying out active experiments on the object (that is, by changing the input in some specific manner), a level of knowledge about the properties of the object may be achieved such that changes in the object’s behavior in response to any given input may be predicted. However, no matter how thoroughly the behavior of a black box is studied, an unambiguous conclusion about the internal structure of the object cannot be reached, since the same behavior may be characteristic of different objects.
The black-box method is widely used to solve problems in the modeling of controlled systems—for example, in the study of integrated systems—especially in cases where the behavior rather than the structure of a system is of interest.