This is really an email to say just how awesome this software really is.  Over the past couple of years I have put together a CNC table for my Plasma, router, engraver, dremel, etc and everthing about Mach 3 has worked flawlessly.  Recently, I had some crashes because I was asking too much of my steppers, so I installed optical encoders on the motors, installed a second parrallel card, and hooked everything up just as recommended and it all worked just as advertised.  With one simple 3 line brain, the system stops if the steppers don't step.  Now I am playing with the custom screens so that they display the encoder DROs next to the motor DROs.  My only regret is that I don't have enough time to really get into everything that Mach 3 is capable of!  You guys rock.

I did not understand what you were asking at first.  Sometimes the meaning gets lost in the translation between languages.  Here is the link to the tutorial videos on Brains.  It is where I learned what they are and how to use them.
http://www.machsupport.com/videos/   Choose "Introduction to Brains"

I hope this helps.