The interrupt mechanism is the means for coordinating multiprogramming between an I-stream engine and the engines of a channel subsystem. An interrupt is a hardware enforced transfer of control within an I-stream engine. An interruption usually takes place after an instruction is completed and before interpretation of the next instruction is started. The logic built into z/Architecture® support is enough to preserve the information necessary to return to the interrupted point of departure. Further, interrupts of the same kind are inhibited generally by the z/TPF system, at least long enough to preserve the state of the I-stream engine and to save control information and data. Ultimately, return is made to the interrupted code without loss of data. Classes of interrupts inhibited in an I-stream engine do not prevent interrupt generating signals to be set in the device controllers and devices. These signals are essentially stacked within the channel subsystem, which presents the signals to any I-stream engine that is willing to accept the interruption.