[BBC-Micro] DFS on 3.5inch - Is this supposed to work?

[Richard Gellman]

Mark Usher wrote:
> Don't forget, when using 3.5 inch drives on a BBC B (not master) with 8271
> controller, to use JGHs patched DNFS ROM.
>   
Ah now, see this is a complication.

What does the patched ROM do that the original DNFS (which is in my 
model B) doesn't? Is this relating to the index pulse suppression 
mentioned in another post? (my apologies to the author for forgetting 
their name...)

-- Richard