A flexible feedback queueing model for a computer system is described. The model consists of a single server and a queue into which jobs are inserted at positions which are functions of their attained service. Special cases of the model include both the round robin and the first-come-first-served disciplines, but a wide variety of other algorithms, having different performance characteristics, can also be obtained. The model is analyzed using Markovian assumptions, and both the finite quantum and processor sharing cases are considered. The relationship of the model to system overhead is also treated.