Quoting Lloyd Zusman <ljz / asfast.com>:

> [ ... ]
> 
> I believe that this mount information would be found under this
> registry key (or under one of its subkeys):
> 
>   HKEY_CURRENT_USER/Software/Cygnus Solutions/Cygwin/mounts

I'm following up to my own message to report that I just determined 
that this is the exact registry entry:

 HKEY_CURRENT_USER\Software\Cygnus Solutions\Cygwin\mounts v2\cygdrive prefix 

The "v2" in "mounts v2" should be the version number of Cygwin.


> This should be a fairly easy fix for rubywin, and it will greatly help
> Cygwin users who change the drive prefix, because at the moment this
> renders rubywin almost unusable to them.

--
 Lloyd Zusman
 ljz / asfast.com