analog

1. Information Science: (1) Phenomenon that varies infinitely over a range. For example, during the early part of a day sunshine gradually increases in brightness in a smooth flow and then decreases in the same manner in the later part. At any given moment, the sunshine is either more or less bright than the preceding and succeeding moments. In contrast, a room lit by an electric bulb is either dark or lighted at any given moment, depending on whether the current is switched on or off. Similarly, the colors and shades in a film-photograph or a painting merge smoothly into neighboring colors and shades, whereas a digital photograph (or a scanned painting) consists of tiny dots each of which is distinct and separate from its neighbor. (2) Correspondence or resemblance of the copy (facsimile or representation) of an item with the item itself. A chart or graph, diagram, photocopy, photograph, picture, or scale model 'looks like' (is 'analogous to') the movement of prices, layout of a building, the original document, face of a person, the shape of a machine the 'thing' it represents. Similarly, analog devices reflect (in one way or the other) the quantities they measure: a mercury thermometer shows a column of mercury that is proportional to the temperature it reads; the 'second' hand continuously sweeps the face of a watch and represents the unbroken flow of time, the needle of a car's fuel gauge indicates amount of gas in the tank by pointing to a corresponding level on a scale. In summary, analog information is (a) continuous, (b) measured, and (c) precise (as opposed to accurate).

2. Communications: One of only two methods (the other is 'digital') of converting data into electrical signals. Analog signals are continuous waves and correspond in magnitude (more or less, high or low) to the quantities they represent. For example, an analog mobile phone converts sound waves into identical electrical waves which are reconverted into sound at the receiving end. Being identical (analogous) to electrical signals generated in nature, analog signals are highly susceptible to interference from natural phenomenon (such as weather and sun spots) that cause signal distortion, loss, and noise. Analog signals degrade with distance and repeated duplication but, for the same amount of data, require less bandwidth for transmission than the digital signals.

3. Computing: Representation of data by a physically measurable quantity that is proportional to the data being represented. An analog computer converts data into a corresponding voltage for data processing, storage, and transfer. For example, a temperature reading (say, 30°C) may be represented by an electric current of 2.5 volts, and twice as high reading (60°C) by 5.0 volts.