Servo track writing (STW) is the process that defines tracks and sectors on the disk platters by creating the servo patterns so that the HDD servo system can later use them to identify tracks and sectors, and to measure the relative position of the read head relative to the center of the track. Accuracy and precision required in the HDD servomechanism have been emphasized, and the associated challenges have been explained in chapter 2 and chapter 3. Performance of the HDD servomechanism is affected by the precision at which the position feedback signal can be generated. The STW process, therefore, plays an important role in making the continuously growing trend of track density a reality.