1. A method of obtaining first and second operand data strings from a memory unit, wherein said first and second operand data strings are utilized in executing an instruction, and wherein said first and second operand data strings each includes at least one operand data word, each operand data word having a predefined format such that a predetermined group of bits of said operand data word defines a digit, said digit being a sign character or a numeric character, and wherein the first operand data word of each of said operand data strings contains a most significant digit, and the last operand data word of each of said operand data strings contains a least significant digit, said method comprising the steps of: (a) loading said operand data words of said first and second operand data strings in a pre-established order in said memory unit; and (b) fetching said operand data words, in sequential order from said memory unit, such that the operand data words of the first and second operand data strings having the most significant digit are fetched first, the remainder of said first operand data words are fetched next, and the remainder of the second operand data words are fetched in a reverse direction, such that the operand data word having the least significant digit is fetched first, thereby allowing a predetermined arithmetic operation designated by an arithmetic instruction to begin on the first and second operand data strings while the second operand data words are being fetched.