Discontinuous molecular dynamics simulations are performed on systems containing 32 hard chains of length 192 at three volume fractions, phi = 0.40, 0.45, and 0.50, to investigate entanglement relaxation and release in model polymer melts. The relaxation behavior of the systems is compared to that predicted by the tube model and to that suggested for the release of interchain entanglements, or knots. The mean squared displacement of the chain center of mass, the mean squared displacements of inner, outer, and intermediate segments along the chain, the end-to-end vector autocorrelation function, and the apparent self-diffusion coefficient are calculated over the course of the simulations. The three relaxation times (tau(e), tau(R), and T-d) predicted by the tube model are estimated in order to determine the extent to which the results exhibit tube confinement. The initial relaxation of chain segments occurs from the ends toward the middle as the tube model predicts. However, different methods for predicting the longest relaxation time, tau(d), provide inconsistent results. An analysis of the mean squared displacement behavior of chain segments at various Positions along the chain reveals when final relaxation occurs and suggests that the final relaxation is occurring at the chain ends, inconsistent with the tube model but compatible with the release of interchain entanglements or knots. A combined analysis of the end-to-end vector autocorrelation function, the outer segment mean squared displacement, and the apparent diffusion coefficient suggests that knot release behavior is occurring in the systems. The results provide support for a proposed mechanism of interchain entanglement relaxation consisting of initial relaxation, followed by memory and final release from a chain end; however, the uncertainty is large at these long times.