Motivated by the attempt to compare performance of certain M/G/1-TS queueing systems under different schemes of assigning jobs to the server, the main result of the paper is concerned with a M/G/1 preemptive resume queue where upon an arrival the job in service is placed at the end of the queue.
The Laplace transform of the steady state distribution of the waiting time W(x) for a job which requires service time x is determined. The variance of W(x) turns out to be less than the variance of this variable in case the service discipline is such that the job in service is placed on position 2 of the queue. As can be shown in the case of exponential service time the variance reduction can be considerable.