Each different card can hold certain amounts of information on the chip..
The Silver holds more than the Emerald, the Emerald Holds more than the Gold.
With that you can therefore programme more or less information onto the card, depending on which one you use...The more info it hold the more you can programme onto it and the more that can go wrong too..lol...
Basically you can use different codes for different cards and add other providers also such as seca and irdeto onto the one card..
Hope that helps...if not check out Cardman's site, he has a very detailed description of the working and make up of each and every card..