A means of modulating a signal to create a quantized and coded form that can be ultimately interpreted as digital data. In the creation of optical discs (such as compact discs and videodiscs), the binary numbers representing the data on the master tape are encoded as a series of pulses. This series of pulses then drives a laser which etches it as a pattern of pits on the surface of the disc. This process is also used to digitally store audio.
In telecommunications, PCM is used to demodulate an analog signal (such as comes over a telephone line to a modem) and glean digital data from it. It does this by measuring the analog signal at a rate of 8000 times per second, encoding each measured unit with eight bits. This works out to a rate of 64,000 bits per second, or 64 kilobits per second. (See also Adaptive Differential Pulse Code Modulation.