Measured and Modeled Responses for Heat-Assisted Magnetic Recording Up to Ultra-High Areal Densities

While current magnetic recording components are still far from able to support user areal densities of 10 Terabits per square inch (Tbit/in<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>), it is nevertheless instructive to examine the behavior of readback waveforms as such extreme densities are approached. Waveforms from a contemporary shingled Heat Assisted Magnetic Recording (HAMR) drive are captured and separated into linear and nonlinear signal components, inter-track interference, signal-dependent media noise, and head/electronic noise. These are tracked and compared with modeled behavior as the raw areal-density seen at the disk surface is gradually increased. The modeled signal and noise are based on the reader response being approximated as the difference of two two-dimensional Gaussians. The raw areal-density measurements range all the way from 1.5 Tbit/in<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> to 12 Tbit/in<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>. At the extreme of 12 Tbit/in<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>, the signal is still clearly identifiable and is well behaved with minimal distortion. It is however completely overwhelmed by high levels of stationary media noise and, to a lesser extent, inter-track interference and then head/electronic noise.