Of course this post is talking about hard disks. The ones with spinning disks and read/write heads flying very close to the spinning disks surface.

There are several links to the source papers and works discussing the findings – take look into this nice rabbit hole:

• An Introduction to the HDD, modelling, detection and decoding for magnetic recording channels
  
• The Study and Development of Automatic Data Acquisition System for Spin-Stand Imaging and Drive Independent Recovery of Hard Disk Data