"More" isn't a meaningful qualifier without a quantifier. I'm not convinced that it would take more than $0.01 worth of resource. I could even see doing it in a purely analog fashion with an extremely basic component like a mosfet. If a pin goes high because the computer responded to your request to send electrons, it sets the corresponding channel.

> So it's probable that the check is sequential.

It's a user unfriendly design for the process to be "send request, wait 5 seconds, send request on next channel, wait 5 seconds, send request on next channel, ..." when it could instead be sending requests across all channels rapidly and then that getting a response on a particular channel _activates_ that channel by analogue means.