1. An apparatus for transferring data among an instruction and operand processing unit, an intermediate storage unit and a main storage unit in a data processing system, the instruction and operand processing unit supplying requests for operands to the intermediate storage unit, the intermediate storage unit supplying, in response to a request, a requested operand to the instruction and operand processing unit or causing a move-in request for the requested operand to be supplied to the main storage unit, and the main storage unit retrieving data including the requested operand in response to the move-in request, the apparatus comprising: move-in means, coupled to receive data retrieved from the main storage unit, for storing the retrieved data pending storage in the intermediate storage unit; storage means, in the intermediate storage unit and coupled to the move-in means, for storing data retrieved from the move-in means for supply to the instruction and operand processing unit; primary means, coupled to the storage means and the instruction and operand processing unit, for transferring requested operands from the storage means to the instruction and operand processing unit in response to requests; bypass means, connected between the main storage unit and the instruction and operand processing unit, for transferring requested operands from the main storage unit to the instruction and operand processing unit before error checking is done in the intermediate storage unit; bypass matching means, in the intermediate storage unit, for matching requests for operands with data which is the subject of a move-in request being retrieved by the main storage unit, and generating a bypass match signal when a match occurs; and control means, connected to receive the requests for operands, to the bypass matching means, and to the instruction and operand processing unit, for signaling the instruction and operand processing unit to receive a requested operand from the bypass means in response to the bypass match signal.