The DFS is remarkable in that unlike most filing systems, there was no single vendor or implementation. The original DFS was written by Acorn, who continued to maintain their own codebase, but various disc drive vendors wrote their own implementations. Companies who wrote their own DFS implementations included Cumana, Solidisk, Opus and Watford Electronics. The Watford Electronics implementation is notable for supporting 62 files per disc instead of the usual 31, using a non-standard disc format. Beyond that, the Solidisk implementation introduced proprietary "chained" catalogues which alllowed unlimited files per disc (only constrained by the disk size). Other features in third-party implementations included being able to review free space, and built-in codice_1 and codice_2 commands, which were shipped on a utility disc with the original Acorn DFS.