Magnetic cores having approximately rectangular hysteresis loops and bistable properties have been used as logic and switching elements for several years. They offer exceptional reliability, flexibility and cheapness for systems not required to operate at extremely high speeds.The principle of current-steering circuits based on ferrite-core and semiconductor-diode combinations has been discussed in previous papers. This paper describes current-steering commutators which steer well-defined current pulses sequentially along a number of paths. Expressions are included which, although simplified, are sufficient to allow reliable systems to be designed, and a practical example is included in the Appendix.There is no general rule to be followed when designing a core device; the choice of core material and size should be decided individually for a particular application. It is always advisable to study manufacturers' published data and to design adequate circuits in view of the inexactness of the assumption that the spread of switching characteristics from core to core is negligible.