We examine the effect of variability on the performance of an assembly system where two stations feed another station and a competing system where two independent stations are fed by a single station. We study the impact of variability in processing times, variability due to unreliable workstations, and variability due to imperfect yield. The above impact is examined for both PUSH and PULL manufacturing environments. We also discuss design features of the two configurations that could be used to recover part of the output lost due to variability.