EMC2 Servo Loop

This is a question mainly for Jon Elson, being the EMC2 guru-

You mentioned in a recent post that EMC2 can run the servo loop in the PC,
which I presume means the PC is reading the encoder outputs. My question is:
how can the PC read the encoder fast enough? I know there are some fairly
significant delays in the parallel port speed, at least on output. Maybe
that's not an issue on input? Also, where do you get enough inputs?

--Phil M.