knock sensor

[Nick Lawrence]

I am trying to understand the workings of knock sensors that are on Audi 100 and 200's.
If knock occurs will it make a fault code? 
Has anyone made a way to get instant readings if knock occurs?
Is changed timing the only action when knock occurs? (just what the ecu can do, not melt down)
Does the knock sensor operate only in a certain rpm band?

In the case of the 100, if there is no noticeable difference in performance or mileage between using regular (87 octane) and super (92 octane) can it be assumed that no knock and therefore no timing adjustment occurred?
No I don't risk running the turbo on anything but super! but it would be good to know if there was ever knock present.
TIA for any insight.
Nick