1. A microprocessor, comprising: a first register file containing registers; a second register file containing registers; and a facility for granting access to the first and second register files in a single thread mode and in a multi-thread mode, wherein, in the single thread mode, a single thread has access to both the first register file and the second register file and wherein, in the multi-thread mode, a first thread has access to the first register file and a second thread has access to the second register file.