A disk drive is disclosed operable to generate an actuator control signal for actuating a head over a disk. A memory address is used to read a first state k variable from a first state variable memory SVM1. The first state k variable is stored in a second state variable memory (SVM2) while processing the first state k variable to generate a first state k+1 variable. The first state k+1 variable is stored in the SVM2, and the memory address is assigned to the SVM2 so that the first state k+1 variable becomes a second state k variable and the first state k variable becomes a first state k-1 variable.