fedora core 4: no fd0u1680?

I've been using core 4 for quite some time now and this is the first 
time i've had to think about device nodes. I'd like to mount a floppy 
that's formatted to 1680 density but can't figure out how the device 
nodes work. Googling has gotten me nowhere (except a lot of Japanese 
pages--apparently this format is popular there).

For starters, there's no fd0u1680. And what are /dev/fd/[0,1,2,3] for? 
Does this have something to do with Udev? I tried and failed to 
understand how that works (or, really, what it is).

I have another box i can use in the mean time, but any pointers would be 
very much appreciated.

b