1. In a data processing system, which includes a central processing unit (CPU) which performs operations according to an instruction, the operations operating upon integer data, a data register system comprising: a first register set including a plurality of first registers each for holding the integer data; a second register set including a plurality of second registers each for holding the integer data and for holding floating point data, wherein the instruction includes a field specifying which of the first and second register sets is to be accessed in response to the instruction; means, responsive to the field, for accessing the first register set or the second register set as specified by the field, including i) reading means for reading an operand value from either the first register set or second register set as specified by the field, and ii) writing mean for writing a result value to the first register set or the second register set as specified by the field.