1. A design structure embodied in a machine readable storage medium for at least one of designing, manufacturing, and testing a design, the design structure comprising: a computer system comprising a CPU; a storage device; circuitry for providing a speculative access threshold corresponding to a selected percentage of the total number of accesses to the storage device that can be speculatively issued; and circuitry for intermixing demand accesses and speculative accesses in accordance with the speculative access threshold.