Servo pattern writing?
Servo pattern writing is like drawing the lines for a piece of graph paper on a blank sheet. Servo patterns are magnetic data written onto the disk surface while it is in the factory, which form the core of the position sensor system for the hard drive’s read and write heads. Based on the servo pattern layout, the user’s data is mapped out on the disk.
The quality of the servo pattern system directly affects how close the data tracks can be squeezed together, which determines how many gigabytes of user data can be packed into each drive. In other words, more terabytes for your money.
The servo system is a core component of any hard drive. The servo system is a motion control system consisting of a voice coil motor, position sensing system, and a microcontroller that enable the position of the heads to be controlled accurately over data tracks to within several nanometers.
Servo pattern writing involves precise control of the head position over the spinning disk surface while the magnetic patterns are being written, and requires advanced control. Spindle rotation, disk flutter, suspension vibration, windage, and random external knocks and bumps all must be controlled for, or else the drive could end up with crooked tracks, degrading the capacity performance of the drive.