Just thought I'd throw this out there.... was browsing the web on real time systems and Mach3, and came across this website:
http://www.intervalzero.com/rtx.htm

Seems to be some sort of addon to Windows XP that allows a programmer direct access to the API and hardware functions in real time. 

Not sure if Mach3 would benefit from this, but using an addon like this would certainly up the price of Mach3.

Comments, anyone?

There are several real time extensions for Windows that date back to at least NT. In fact the first PC based CNC control I ever laid hands on was NT based. Even though they can provide deterministic real time operations they are usually an expensive option and more highly dependant on the underlying hardware. Even though such a system is deterministic it is still limited by the underlying PC hardware which is not designed to be hard real time. I think Mach has prospered because it provides good performance at a low cost and low enough complexity level that most folks can install and use it.

IMHO the plethora of external motion control boards is the future of Mach.

Thanks for the insight.

Interesting you mention the motion control cards.   Does the Galil card act as a buffer between Mach3 and the servos?  I mean, does it store the pulses and generate it's own timing so you would not have to worry too much about Windows XP processes interfering with Mach3?

Are there any cards out there that buffer and generate their own timing for ultra smooth operations?

Mach 'pre plans' the moves that needs to be made and makes this pre-planned buffer available to motion control plug-ins. The plug-in will package up the movements in the buffer in the fashion needed for that particular motion control card and send it to the card. The motion controller will will buffer a small number of moves to negate and delay due to the time it takes to transport the data. The motion controller then outputs the needed step pulse to get to where Mach tells it to go. Since the motion control card does all this in dedicated hardware the result is a much more stable (smoother) and faster (potentially) than you can get through the parallel port.

The motion control cards that work with Mach all have different abilities. The Galil comes in several flavors and can ran analog servos as well as digital servos and steppers, they are really capable units and generally more expensive than other options. The SmoothStepper will work with stepper and digital servos (S/D input), it was designed to interface with Mach and is at the other end of the cost scale. The other motion board that work with Mach are in between these two.