1. A data processor comprising: a set of special-purpose registers; a set of general-purpose registers; an execution unit for executing a superword transfer instruction for transferring data between memory and said set of special-purpose registers and said set of word-sized general-purpose registers so that some of the data transferred is located in one of said general-purpose registers and some other data transferred is located in said set of special purpose registers, said instruction specifying said general-purpose register explicitly and said set of special-purpose registers.