at this position although automatic controls can be employed the data processing system operator will typically know how much data is to be transferred and will simply arrange for shutdown after the completion of data transfer to a given number of cassettes with a maximum of eight to start the sequence of successive insertions of cassettes 24 into the tape drive 26 the transporter mechanism 46 is first positioned in line with the exit level 42 of the cassette tray 36 fig2 while the cassette associated mechanisms are in wait mode positions in this mode the lifter brackets 97 98 are in the lowered position and the end tab 144 and the cartridge advance mechanism 130 are at their rearward positions when the height position sensor 56 fig1 indicates that the cassette holder 52 is in alignment with the exit aperture 42 the sequencer 58 operates the cassette advance mechanism 130 fig8 through a cycle in this cycle the motor 132 and coupled lead screw 136 are first driven to shift the cassette 24 in the upper level forwardly by one cassette dimension in the front rear direction the rear cassette thus moves to leave a gap as the forward cassette is moved into the cassette holder 52 in the transporter 46 the lateral shifter 60 may be used for final adjustment of cassette position by engaging the lip or acting as a stop the cassette advance mechanism 130 then returns to its wait position the available empty cassette position at the rear of the upper level is thus available to be filled by the rear cassette in the lower row however this can be done during the wait.