"gauge ensemble" are Markov Chain Monte Carlo datasets containing random space-time configurations of the chromo-electromagnetic field. Each folder contains one or more chains. They are generated using the most powerful supercomputers and constitute the basic data structure for Lattice QCD computations. The data available here has been donated by different research groups, they are are stored in the NERSC HPSS. Different groups use different file formats to store the ensembles. Here is a script to detect and convert file formats.