X11 Optimizations?

[james cerrato]

We are building a graphics application using X11R4 and are using
     X Window System - C Library and Protocol Reference
          by  Gettys, Newman and Scheifler
as our guide to using X.  In the introduction it states
   "For the best performance, when the client and server reside on the same
    machine, communication between them is often implemented using shared
    memory."

I have asked other X programmers and they don't know about this.  The question
I have is if this 'shared memory' communication is something that the
application builder must specify in some way (and how?) or if this is
done by the X Server without any changes in an application.

Thanks in advance for any info on this subject, or any related info about
how to optimize X applications.

James Cerrato
Associative Design Technology
508-366-9166
adt!james at bu.edu