The Pad Thai most traditionally and commonly found at street stalls, food courts and open air markets, is made with dried shrimp. Competition drove many vendors to go high end by using fresh shrimp (Pad Thai goong sod). This pad Thai recipe is for the older, more traditional version.
When I was growing up, my uncle was in charge of getting everybody late night snacks. He would go out to the nearest all night market and come back with everyone's orders. Mine was always Pad Thai. The pad Thai came wrapped in an old newspaper page lined with a plastic sheet. They would put extra sugar and ground chili pepper between the newspaper and plastic sheet. You don't see such make-shift food wrap anymore; now it's in a foam box.