  We report on the development of a trapped-ion, microwave frequency standard
based on the 12.6 GHz hyperfine transition in laser-cooled ytterbium-171 ions.
The entire system fits into a 6U 19-inch rack unit ($51\times49\times28$ cm)
and comprises laser, electronics, and physics package subsystems. The
performance of this development system is evaluated; the fractional frequency
instability was measured to be $3.6\times10^{-12}/\surd\tau$ for averaging
times between 30 s and 1500 s.
