Thank you for a very informative tutorial.
I notice that the author of Spinrite claims to be able to influence the behaviour of the AGC circuit in a drive's read preamp. He does this by training the AGC circuit with a data pattern designed to produce a maximum flux amplitude, and then following it up with a minimum amplitude flux pattern. He claims that this technique will uncover weak sectors.
Here is Steve Gibson's explanation:
http://www.grc.com/srphysics.htmYour tutorial includes the following picture of a modern data sector:
http://en.rlab.ru/doc/images/HDD_Tracks_and_Zones/data.jpgI'm wondering whether the read gain established during the AGC preamble persists throughout the entire data sector, in which case Gibson's claims would no longer be true, assuming they ever were. Or is the AGC active throughout the entire data field, in which case the gain could vary?