How does a mesa card handle so many inputs?

Does it switch between input and output or just the firmware they use?

I'm just kind of curious. I know they generate step pulses thru hardware

Peter is much more qualified to answer that.
I think i read that they can handle up to 4096 IO and some other things.

A lot of our breakout cards use serial interfaces running at 2.5 Mbaud
(7I70,7I72,7I72,7I73,7I76,7I77,7I84 etc)

These use our SSerial interface that allows discovery of hal pins by the driver
automatically. The base FPGA card can support up to 32 of these interfaces
each with up to 96 bits of input and output data in real time

its the Magic inside the Box

PCW wrote: The base FPGA card can support up to 32 of these interfaces
each with up to 96 bits of input and output data in real time

I wonder how many cards LinuxCNC can support? I had a quick look through the headers to find out and found:

github.com/LinuxCNC/linuxcnc/blob/master...tmot2/hostmot2.h#L74

I wonder if that means that there can't be more than 1000 hotmot2 pins?

Looks like it, I think the max I've seen is in the 700 region
Probably not much cost associated with increasing that if needed