I am hoping that a member who works in the banking security area might be able to answer a security related question.

With regard to credit and debit card four-digit PINs that we are expected to memorize, do the Banks, or perhaps more correctly, Visa / Mastercard, store that PIN number in their card info database as plain text numbers, a one way hash, a reversible hash, or some other way?

To be clear, I have no interest in attempting to crack or figure out what a card's PIN is, just understand how that piece of info is stored.

Thanks.