  In this work, approximate and exact results concerning a performance measure
of the MGinf system, the age or the excess of the busy cycle, are presented. It
will be seen that it is also a measure of the busy period performance. Service
distributions for which it is given for a simple expression and others for
which this does not happen are considered. For this last case, bounds are
deduced. A special emphasis is given to the exponential distribution and to
those related with it, useful in reliability theory.
