Code rate of constrained code for phase change memories

Non-volatile memories, e.g., flash memories and phase change memories (PCM), have been widely used in computers and especially mobile computing devices because they have no mechanical components, they consume less power, and the access speeds of them are very high in comparison with hard disc drives. In magnetic recording systems, constrained codes are used so that stored data sequences are easily and correctly retrieved. In storage systems using non-volatile solid state memory, the constrained codes may also be employed but for different input constraints, e.g., (α, β, p)-constraints introduced by A. Jiang et al. [4]. In this paper, two code construction methods for the (α, β, p)-constraints for PCM are given. Next, a new constraint for PCM is introduced so that a constrained code with a higher code rate can be constructed from the constraint.