In digital transmission, wave patterns are translated into discrete bits and are separated by intervals. Bits (contraction for binary digits) are the smallest unit of information in data processing. They may be compared to a light-bulb, which is either on or off. When the bulb is on, information is being transmitted; when it is off, there is a blank or interval. In the figure, the upper line of the rectangular wave form represents the bits. The lower line denotes the interval between bits. At this juncture, it must be noted that all electronic transmission can occur in either the analog or the digital mode. The telephone network, originally intended to carry only the human voice, operates mostly in the analog mode, althoughall-digital transmission is now available as well. Digital transmission has the advantage of being entirely compatible with computer and terminal originated messages, which also operate in digital mode, and of having the capability of transmitting messages more accurately than the analog mode.