Just to get my mind straight:
The 'Interface' is the device that is connects the 'Controller' to the computer via a parallel port, USB or ethernet cable, such as a BOB.
The 'Controller' is a collection of devices (hardware) that comprise circuitry that facilitates functions such as:
Limit and home switch inputs – more IO ports allows separate input of switches to help with troubleshooting.
E-Stop input
Stepper motor drives
Relays for Spindle On/Off - direction, Coolant, etc
Analog output for spindle speed
Probe – set tool height
MPG – manual pulse generator to manually move the axes
LASER
and there are 'Power Sources'.
Both the 'Interface' and the 'Controller' hardware has to be built to allow particular software such as Mach3 or 4, or any other chosen software.
The Computer, Power Sources, Interface and Controller have to be electrically isolated. In fact, there are Interface and Controller components and parts of their circuitry that should not have a common current flow. 'Energy or information can still be exchanged between the sections by (other) means such as capacitance, induction or electromagnetic waves, or by optical, acoustic or mechanical means' (wikipedia), and these 'means' are built into all the devices.
I would like to maintain all the functions my CNC has at present, inclusive of MPG, as a minimum. I'll also keep my motors and their Encoders as they seem to be working well at present. My router does not have a coolant facility, but who know, might need it in future.
Please advise which Windows O/S would be most stable for Mach3. I presently run on Vista, but maybe another would be more stable?