Welcome to brain Stuff from how stuff works dot com where smart Happens. Hi, I'm Marshal Brain with today's question, how does the magnetic stripe on the back of your credit card work? The front of your credit card contains your credit card number. If you look at this number, the first digit is called the system number. The next five digits are a unique I D for your bank, The next eight digits are your actual account number with that bank, and then the final digit is a check
digit for error detection. The stripe on the back of the credit card is a magnetic stripe, often called a mag stripe. The mag stripe is made up of tiny iron based magnetic particles in a plastic like film. Each particle you could think of as a very tiny bar magnet, about twenty millions of an inch long. The mag stripe can be written because the tiny our magnets can be magnetized in either a north or a south pole direction.
The mag stripe on the back of the card is very similar to a short piece of cassette tape fastened to the back of the card. Instead of motors moving the tape so it can be read, your hand provides the motion as you swipe the card through a reader or inserted in a reader at a gas station pump. There are three tracks on that mag stripe. Each track is about a tenth of an inch or two millimeters wide.
The I S O I e C Standard seven eight one one says what will be on those tracks, and it specifies that the first track holds seventy nine six bit plus parity bit read only characters, Track two holds forty four bit plus parity bit characters, and track three holds a hundred and seven four bit plus parity bit characters. This means that the first track can have alphabetic letters in it, while the others have only numbers in them. Your credit card typically uses only tracks one and two.
Track three is a ReadWrite track that includes an encrypted pin, country code, currency units, and things like that, but it's usage isn't standardized among banks, so it can't be used
that well. The information on track one is contained in two formats, A which is reserved for proprietary use to the card issuer, and BE, which is standardized and includes the primary account number up to nineteen characters, a country code of three characters, a name in alphabetic characters from two to twenty six characters long, and then an expiration date or a separator four characters or one character. The format of Track two can only contain numbers, and it
was developed by the banking industry as follows. The first part of it is a primary account number up to nineteen characters. The second part is a country code of three characters, and then there's a expliration data or a separator of four characters or one character. There are three basic methods for determining if your card is going to be able to pay for what you're charging. In the first method, merchants with a few transactions each month do
voice authentication using a touch tone phone. They call up the card company and they can talk to a human being if they need to. The second method, which is far more common, is electronic data capture or e d C, using mag stripe card readers like you see in stores today or on gas pumps. These terminals can either call up individually using a modem, or they can send their data to a computer system that does the checking, and
then there's virtual terminal on the Internet. If the card reader isn't able to accept your card, it's either because it can't read your card or because the card company has rejected it. If it can't read your card, it could be because of a dirty or scratched mag stripe, or, more likely, an erased bag stripe. The most common causes for erased bag stripes are exposures to magnets like the small ones used to hold notes and pictures on the refrigerator, or exposure to r f I D readers. Do you
have any ideas or suggestions for this podcast? If so, please send me an email at podcast at how stuff works dot com. For more on this and thousands of other topics, go to how stuff works dot com and be sure to check out the brain stuff blog on the how stuff works dot com home page