Suppose we have the following model for digital control of the disk drive.

Now we can enter the model for the disk drive's continuous transfer function.

 First we will enter the mathematical model for the disk 
 drive. We use a simple second order model for this system.
 The inertia of the head assembly I=0.01 kg-m^2,
 the viscous damping coefficient C=0.004 N-m/(rad/sec),
 the return spring constant K=10 N-m/rad, and the motor
 torque constant Ki=0.05 N-m/rad.

 >> I=0.01; C=0.004; K=10; Ki=0.05;
 >> sys = tf(Ki,[I C K]);