In synchronous lines the movement of jobs is coordinated; all jobs move to the next work station simultanuously. So the number of jobs in the system remains constant, and there is no need to put buffers in between stations. This type of production line may be further split up between paced and unpaced lines. In asynchronous lines the movement of jobs is not coordinated. The operator or machine starts to process the next job as soon as one becomes available. And on service completion the job immediately moves to the next work station, as long as there is space for it. Thus an operator or machine can become starved (no job available) or blocked (no room to put a completed job). Asynchronous lines are almost always unpaced. The number of jobs in the system may fluctuate (considerably) and buffers are needed to prevent starvation and blocking (i.e., loss of capacity) as much as possible