Address literals used pointers?

["Steve Dondley" <stevedondley at attbi dot com>]

Hi,

I know this is more of a C type question that a gcc question.  If anyone can
recommend a good mailing list for basic C questions, I'm all ears.
Anyway...

I'm reading Kenneth Reek's excellent "Pointers on C".  On p. 291, there is
some code that I'm a bit stumped by:

#define DISK_REGISTER	(unsigned int *)0xc0200142
*DISK_REGISTER &= 0xfffffc1f;

This *DISK_REGISTER expression appears to perform indirection on a literal
cast as a pointer.  Is this an accurate description of what's happening?
Can someone point me to a place where I can learn more about this cast?

I want to learn more but the syntax isn't explained in the book and Google
isn't helping.  I can't duplicate the code because I keep getting a
segmentation fault when I try it out and so I'm curious to know how one can
get a bit of code like this to work without causing a segmentation fault.
Does the operating system designate some addresses (driver addresses, for
instance) outside the bounds of program memory as writable?