Continuing this series of videos, we explain fundamentals of HDD theory of operation. Main interest lies in how the position error signal is obtained to understand its nonlinear nature and its limitations. The video illustrates the basic components of a hard disk drive: spindle motor, voice coil motor or actuator, disks, arms and read/write heads. It also explains how the data is stored in and retrieved from tracks and how the disk is divided in servo sectors and data sectors. Every track has sectors of data and servo. The servo sectors contain the servo bursts used to detect the position error signal with respect to the center of a track. Watch the video if you need a quick and efficient acquaintance with the HDD theory of operation. This video illustrates the characteristics of our particular application. It’s needed to understand the restrictions for the robust control.