The inside of a 2403 tape control unit. The panel on the left contained a kind of pegboard where pins were inserted to specify a tape command, after which hitting one of the small silver buttons would execute it. We used it mainly to write tape marks (a character that delimited files, indicated end of file, and so on) because it was quicker than running between the CPU and the tape drives. Any tape command could be entered and executed here without any involvement of the computer itself.