Data on the Credit Card is stored on Track1 and Track2 on the magstripe
Source: What data is stored on a payment card's magnetic stripe?
Both Track 1 and Track 2 contain enough basic information for processing payment card swipes. Most card readers will be able to read both Track 1 and Track 2 data, in case one of the tracks has become unreadable.
Source: What data is stored on a payment card's magnetic stripe?