limit/home switches

Question for you EMC guys - do the various switches need to be opto-isolated
from the parallel port, or can the simply be hooked directly to their
respective pins?

Does the parallel send/receive 12 or 5 volt signals?

If 12v, can one power the switches from a seperate power supply and hook
them to the individual pins, i.e. pin 10 for the limit switch? I can get 5v
from the same power supply easily enough, assuming the switches already on
my mill (series one cnc) are 5v.

Sorry for the seemingly silly questions, guys, just trying to figure out the
rest of this EMC setup!

Thanks,

Matt King