The first Series of X101 coming of the Assembly lines at FACTORY, that are able to sleep.
Since the 719 series real sleep was introduced. All Sentmacs since then could no longer function around the clock and would feel tired and fatigued, only a power down phase restored peak levels.(*)
(*) Note : Because of this reason it is that Cirruit sleeps as much as he can. As part of his personality simulation he is even more tired than other X101’s that came of the same assembly line.