Media Noise vs. Electronics Noise 
Distinguish Between Them 

As disk drive manufacturers continue to increase disk drive capacity by reducing track width, msnr will get worse

For this analysis, sector-based data is required. The signal structure must contain a single frequency preamble, an address mark field, and a data field. The data needs to be a single frequency pattern. The ideal “data” pattern is a single 2T pattern or equivalent. By utilizing a single frequency data pattern, any hardware channel can be used — PR4, EPR4, E2PR4, or even modified PRML.

Head signal amplitude is approximately proportional to track width. Media noise is approximately proportional to the square root of the track width. Therefore, the ratio of the head signal to the media noise (msnr) is proportional to the square root of the track width. As disk drive manufacturers continue to increase disk drive capacity by reducing track width, msnr will get worse. Although advanced head technology (i.e., MR and GMR) can increase the head signal output for a given track width, the effect of media noise on the head signal is also increased, so there is no improvement in msnr. 
Media noise can affect a disk drive signal in a number of different ways. It can distort the pulse width and amplitude. It can cause either early or late timing transitions and partial erasure. 
The trend is clear: msnr continues to get worse, and as a result, the industry is shifting from designs that were electronics noise- dominated to designs that are media noise- dominated. LeCroy offers new, simple tools to help determine if your system is electronics- or media noise–dominated. One of the key attributes of media noise is that once it is recorded on the media, it is the same on every read. Thus, media noise is repeated noise. 
With the DDA 260, you can optimize your product by identifying the amount of media noise and electronics noise.

The squared sigma of the total noise distribution is the sum of the squared sigmas of the media noise and the residual noise distributions. After multiple acquisitions, residual noise averages away, yielding the media noise.

Examples of how media noise can distort the actual transition. Transition A vs. Transition B is an example of pulse width and amplitude distortion. Transitions C and D are examples of timing distortions. Transitions E and F are examples of partial erasure.