Re: Newbie question
So maybe an expert will chime in after but...
Linuxcnc can I believe run without a Break out board (bob) but a Bob makes connections easier and might add functionality. Alternatively you could use arduino/grbl (or tinyg) which is kind of via USB.
Both would then feed step and direction to stepper drivers (which vary from cncshield v3/v4 types to standalone drivers like geckos, leadshine, and many others. The steppers would be powered by a separate power supply 12v to 80v (24v is common) depending on what the max your drivers can handle and your preference.
Limits would be wired on to the Bob, cncshield or straight to the db25 printer cable depending on the route you take.
Not sure about the Linux or usb. Usb is not recommended for actually controlling a cnc but it can be used to interface with say an arduino running grbl or another control board (which in essence are then little computers combined with a break out board sort of like tinyg).
Linux in itself doesn't run anything and could run Linuxcnc or a program that sends files to a grbl system.
I'm sure there are many other variations too...
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In case anyone is wondering, I'm the twin of the other gfacer on cnczone...