The servo signals are written using special equipment (a precise head/servo mechanism, not the regular HDD heads). You can see them in this magnetic image - th

The servo signals are written using special equipment (a precise head/servo mechanism, not the regular HDD heads). You can see them in this magnetic image - the whole 25% to 75% of the image is the servo signal area. The tracks are seen on the bottom 20%, top 80%: https://commons.wikimedia.org/wiki/File:Aufnahme_einzelner_Magnetisierungen_gespeicherter_Bits_auf_einem_Festplatten-Platter..jpg https://commons.wikimedia.org/wiki/File:Aufnahme_einzelner_M... Bottom to top: - sync (the regular lines) - positional track number, gray encoding (irregular lines) - track fine tune (the block trio) - fine track ID After fine track ID is read correctly, the position is deemed correct, the RX head is turned off, and the TX head is turned on. This is the rx-tx gap. Then track data starts.