Optimal head design and characterization from a media perspective

As the areal recording density increases at a 60% annual rate, it becomes a challenge to design a head that achieves media noise limited recording performance. Since the noise of thin film media is recording-wavelength-dependent, a pseudo-random sequence (PRS) pattern is proposed for the characterization of the signal-to-noise ratio (SNR). This allows for a fair comparison of the media and head noise at the Viterbi decoder input. Extracted di-pulse response measurements indicate that the nonlinear distortion (NLD) at high recording density is not necessarily dominated by partial erasure of the media. Magnetoresistive (MR) read head distortion and write head flux rise time may play a significant role. A method to estimate the bit error rate (BER) from component level SNR and NLD measurement is described. Contributions of head noise, electronic noise, media noise and NLD to the root mean square (RMS) error and BER for today's typical disk drives are analyzed. With the advancement of head and media development, future head requirements to achieve media-noise-limited recording are also discussed.