I for myself think I understand it a little bit........mach3 will drive servo or stepper drives (my Main focus has been dc brush servo's) the larger machines which are most commonly available for retrofit are 3 axis dc servo machines. I have 2 which are very similar. a Bridgeport boss machine and a Lagun 40 taper 3 axis
cnc machine. Gecko's will not run this class of machine 140 volt 14 amp continus dc servo's (peak draw 52 amps) currently there are 3 brands of servo controllers available (that I am aware of ) rutex, Larkin-Viper and Glentek. Glentek only wants to sell servo and drive packages setup to run with Mach. the Rutex don't seem to have enough capicity at this level which leaves the Larkin Viper servo drives. which I plan to use on the Bridgeport boss machine I am currently working on.
the closed loop question is a little different one. the servo's are closed loop back to the servo drive and In larkin's case they have a soft alarm that can be fed back to the software to allow the control to know there is a problem before it crashes the system. so mach 3 is not a true closed loop software it can run servo drives that will let the software know when they are being driven too hard.
also mach3 has been made to run with the galil cards which closes the loop back to the controller card in the computer.
In non Industrial setting I feel like that the mach system running on a knee mill is a much better system than the industry standard Prototrak systems which have probably cut a half a billion parts or more.
for me this has been a learning experience. I feel the support forums are the one plus that none of the other systems have or can come anywhere close to
I hope this helps muddy the water even More =-)
Happy Hunting
archie =) =) =)