IBM 5150 Technical Reference page 283

communication equipment) to analog signals that are suitable for
transmission in a telephone network. The inverse function is also
performed by the modem on reception of analog signals.
modified frequency modulation (MFM). The process of varying
the amplitude and frequency of the 'write' signal. MFM pertains
to the number of bytes of storage that can be stored on the
recording media. The number of bytes is twice the number
contained in the same unit area of recording media at single
density.
modulation. The process by which some characteristic of one
wave (usually high frequency) is varied in accordance with
another wave or signal (usually low frequency). This technique is
used in modems to make business-machine signals compatible
with communication facilities.
modulation rate. The reciprocal of the measure of the shortest
nominal time interval between successive significant instants of
the modulated signal. If this measure is expressed in seconds, the
modulation rate is expressed in baud.
module. (1) A program unit that is discrete and identifiable with
r--.....
respect to compiling, combining with other units, and loading. (2)
A packaged functional hardware unit designed for use with other
components.
modulo check. A calculation performed on values entered into a
system. This calculation is designed to detect errors.
monitor. (1) A device that observes and verifies the operation of
a data processing system and indicates any significant departure
from the norm. (2) Software or hardware that observes,
supervises, controls, or verifies the operations of a system.
most-significant digit. The leftmost (non-zero) digit. See also
high-order position.
ms. Millisecond; 0.001 second.
multiplexer. A device capable of interleaving the events of two or
more activities, or capable of distributing the events of an
interleaved sequence to the respective activities.
Glossary-22