The invention concerns a system for saving data derived from a mainframe characterized in that it comprises a computer equipment including an input/output interface for exchanging data with the guest computer, said interface comprising a backup document reader/inscriber emulator, at least one intermediate storage device and a tape document reader/inscriber, the equipment further comprising a processor for transfer between the input/output interface or the intermediate storage device and the key-to-tape reader/inscriber, the system further including a supervisor comprising a storage unit for recording data concerning key-to-tape recordings of the computer equipment, and for controlling said computer equipment according to instructions coming from the guest computer.