The single-stream program switch is shown in the following
figure.
Program A switches to program B, and Program B switches to Program
C, which then inserts back to the I/O PCB. This model of program
flow delivers the send-then-commit output message successfully. Single-stream
means that the program switches occur one after another. No express
PCBs are used in the P2P message switches. Figure 1. Single-stream program switch
