How Does Information Get Stored in a Credit Card?

The Magnetic Stripe or Magstripe

Credit cards--like hotel keycards, some I.D. cards, ATM cards or other bank cards--often have a magnetic stripe, commonly referred to as the magstripe, on the back. Data are stored on the magnetic band to be retrieved later by a card reader. This magstripe can be compared to a piece of cassette tape that is fastened to the back of the card. Swiping the card through a magnetic reader provides the motion needed so that the information on the tape can be read. Special software is required to magnetically write data onto a magstripe. Information to be read is recorded in an alpha-numeric or barcode format.

Reading the Tracks

The magstripe is made up of tiny bar magnets contained in a plastic-like film. This magnetic tape, an easy and basically inexpensive technology, is the method used for data storage. Data are stored according to the orientation of the magnetic particles. There are three different tracks (or magnetic lines) on the magstripe used for holding encoded information. Credit cards basically read tracks 1 and 2. The information contained on the tracks must conform to the appropriate format in order to be read by the card issuer for the purpose of authentication. Encoded information includes the cardholder’s name, primary account number, expiration date and service code

Writing Data to the Magstripe

Different fields of energy are used to write data onto the magnetic stripe on the back of a credit card. Low coercivity means that a low energy field is used for encoding, and is best used for non-critical security applications. High coercivity uses strong magnetic field energy to write data onto the magnetic stripe, and is necessary for more critical security applications where data on the magstripe must remain encoded for a longer period of time.

Problems Reading a Magstripe

If your card has a dirty or scratched magstripe, or a magstripe that has been erased by exposure to magnets, it may not be accepted. The point of sale hardware (magnetic stripe reader) may not be able to decode the data on the card. To be read successfully, the surface of the magstripe must be smooth and free of dust.