Such a PC is central to the von Neumann architecture. Thus programmers write a sequential control flow even for algorithms that do not have to be sequential. The resulting “von Neumann bottleneck” led to research into parallel computing,[11] including non-von Neumann or dataflow models that did not use a PC; for example, rather than specifying sequential steps, the high-level programmer might specify desired function and the low-level programmer might specify this using combinatory logic.