We describe simulations of a polymer melt sample containing 640 chains, each chain being composed of 100 methylene groups. Using these large scale simulations radii of gyration have been calculated with a statistical error of similar to 2%. At this level of precision it is shown that even for this modest chain length configurational equilibrium is not achieved in less than 4 ns at 500 K. Values of the square radii of gyration, square end-to-end distances and proportion of conformers at equilibrium show good agreement with predictions of the Flory model of alkane chains in which all long range interactions along the chains are ignored. These simulations were performed using a Fujitsu AP1000 massively parallel processing machine with 1024 processors in conjunction with a recently described domain decomposition molecular dynamics algorithm [D. Brown, J. H. R. Clarke, M. Okuda, and T. Yamazaki, Comput. Phys. Commun. 83, 1 (1994)] capable of handling systems containing rigid bond constraints and three- and four-body potentials as well as nonbonded potentials. Detailed comparisons are made with previous accurate data obtained for smaller samples containing just 10 n=100-site chains using the alternative cloning method of parallel processing [D. Brown, J. H. R. Clarke, M. Okuda, and T. Yamazaki, J. Chem. Phys. 100, 1684 (1994)].