A renaming register file complex for saving power is described. A mapping
unit transforms an instruction register number (IRN) to a logical
register number (LRN). The renaming register file maps an LRN to a
physical register number (PRN), there being a greater number of physical
registers than addressable by direct use of the IRN. The renaming
register file uses a content addressable memory (CAM) to provide the
mapping function. The renaming register file CAM further uses current
processor state information to selectively enable tag comparators to
minimize power in accessing registers. When a tag comparator is not
enabled it remains in a low power state. A processor using a renaming
register file with low power features is also described.