1. A computer comprising: a processor having at least one execution unit; data storage circuitry comprising a plurality of register stores, wherein each of the register stores has a predetermined bit capacity addressable by a single address; an instruction fetcher for fetching instructions to be executed by the at least one execution unit; a processor processing operands stored in the data storage circuitry, wherein the operands are represented by data strings, each of the data strings comprising a plurality of sub-strings of discrete data representing objects within the operands, said sub-strings comprising a first sub-string, a last sub-string and at least two intermediate sub-strings, each sub-string comprising a plurality of bits and having the same bit length, said instructions to be executed by the processor including at least one data string restructuring instruction, the at least one restructuring instruction defining the number of bits in each object and being operable on a data string to retain both said first and last sub-strings in unchanged positions and to exchange with each other the positions of at least two intermediate sub-strings in a restructured data string.