Motor_positions.bck contains the date and time of its creation and the motor positions, which are logged in the format of calibrate commands. This means that the log file can be executed with a run command to reset the motor positions.
If ONLINE terminates normally, it produces a new version of the device list making the motor log file obsolete.
Before ONLINE opens motor_positions.bck it renames the old version to motor_positions_iiii.bck.