Magnetic Stripe On A Credit Card

The magnetic stripe on a credit card – or mag stripe – holds enough information to identify you, to inform the bank of all the information needed to process transactions and to let the seller or merchant know that the card is valid and has enough credit to cope with the amount you are charging to it.

Each mag stripe has three tracks of data, each track being one-tenth of an inch wide. Each track is a plastic film in which are embedded iron-based magnetic particles about 20 millionths of an inch long. These particles can be magnetised to face either the north or south pole, which is why the tracks can carry digital information.

First Track

The proprietary information of the credit card company, the A format, is held on the first track along with the B format which contains this information:

1. One character – the start sentinel
2. One alpha only character – format B code
3. One character – a separator
4. Three characters – the country code
5. Two to 26 characters – your name
6. One character – a separator
7. One to four characters – either a separator or the expiration date
8. Up to 79 characters – discretionary information
9. One character – the end sentinel
10. One character – LRC (longitudinal redundancy check)

Second Track

The second track on the magnetic stripe on a credit card was designed by the banking industry. The information it holds is:

1. One character – the start sentinel
2. Up to 19 characters – the primary account number
3. One character – a separator
4. Three characters – the country code
5. One or four characters – either a separator or the expiration date
6. Up to 40 characters – discretionary information
7. One character – LRC

Third Track

The third track on mag stripe can be read and written to, but there are no standard rules on what information it can contain.

Damaging The Magnetic Stripe On A Credit Card

Having your card too close to a store tag demagnetiser or the fridge magnets can cause it to malfunction. The same could happen if the magnetic stripe on a credit card is dirty or has been scratched. Under these circumstances, the card cannot be read.

Validating Your Card

The most common way to validate your credit card and therefore the transaction is by swiping the card through a magnetic stripe terminal. But merchants who have very few transactions use voice authentication through a touch tone phone. The third way to authenticate the card is through a virtual terminal. This method is used for online transactions. So the message is clear – that simple little magnetic stripe on a credit card holds a ton of valuable information and you should take special care of it.