  The KEK 8-GeV electron / 3.5-GeV positron linac has been operated with very
different beam specifications for downstream rings, KEKB, PF and PF-AR. For the
reliable operation among these beam modes intelligent beam switching and beam
feedback systems have been developed and used since its commissioning.
  A software panel is used to choose one of four beam modes and a switching
sequence is executed in about two minutes. Most items in a sequence are simple
operations followed by failure recoveries. The magnet standardization part
consumes most of the time. The sequence can be re-arranged easily by
accelerator operators. Linac beam modes are switched about fifty times a day
using this software.
  In order to stabilize linac beam energy and orbits, as well as some
accelerator equipment, about thirty software beam feedback loops have been
installed. They have been utilized routinely in all beam modes, and have
improved its beam quality. Since its software interfaces are standardized, it
is easy to add new feedback loops simply defining monitors and actuators.
