written to the card is simply a number. A long one, but just a number nonetheless. The number is read by the reader in the slot machine, which then accesses the casino's slot card club database and finds your name and displays it on the slot machine reader and starts keeping track of you.

Where smart cards are being used, it can be a different story all together, because smart cards have the ability to store large amounts of data.

But for mag-stripe cards, its just a number string.

Jim Follis