One interesting feature of the BiiN was that the CPU sets could be used to provide either fault tolerance, as in the Tandem systems, or parallel processing, as in the Pyramid and Sequent systems. This allowed users to tailor their systems to their needs, even on the fly. The BiiN systems also provided two versions of fault tolerance. In "fault-checking mode", processors were paired so that they could check one another's calculations. In event of an error, the processors would stop, and the circuitry would determine which was faulty. This processor would then be excluded from the system, and the computer would restart. In "continuous operation mode" the fault-checking pairs were duplicated, so that if an error occurred the second pair could immediately take over the calculations.