Hi, F_khalaj
Not an Expert myself, Hears some Info to digest:
Q 1. Mach3 is setup for two port's (printer) as shown in Config, Ports & Pins Port 1, 12 outs, 5 ins, Port 2 the same, Except you can change pin's 2-9 to ins giving you 8 more inputs.
There was a little discussion about adding a PCI input/output card, Never was a consensus on which one to use, Thy wouldn't be used for driving any additional Axises though.
Then Brain's (Faster Responce to In-Outs came along , serial or TCIP Interface for PLC's and such.
Q 2. Mach3 likes a clean windows install "dedicated system" to run the smoothest, Theres a Optimization File, Around hear some where. QuickTime and some other programs can cause some problems
Q 3. For the most part Mach3 relies on your Servos or stepper control to carry out it's instructions, I now of at least one board that tracks the differences between Mach3 and position error/feedback from encoders with stepper or servo's
Q 4. G100 (EtherNet, SmouthStepper (USB), NcPodc (USB), Galil DMC Series (not sure PCI), Use dedicated on board CPU control's that Mach communicates/controls.
Hope this Helps, Chip