David RossDavid Ross 522 bronze badges one 1 The SUB is undoubtedly an artefact of CP/M, exactly where it had been used being an EOF marker (CP/M "duration" was blocks, not bytes). MSDOS was created in order to browse CP/M files, & since it was possible at time that CP/M could be utilized to go through the resuts from MSDOS, the ability to control