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Speaker 1: Welcome to brain Stuff from how stuff works dot com

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Speaker 1: where smart Happens. Hi, I'm Marshal Brain with today's question,

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Speaker 1: how does the magnetic stripe on the back of your

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Speaker 1: credit card work? The front of your credit card contains

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Speaker 1: your credit card number. If you look at this number,

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Speaker 1: the first digit is called the system number. The next

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Speaker 1: five digits are a unique I D for your bank,

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Speaker 1: The next eight digits are your actual account number with

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Speaker 1: that bank, and then the final digit is a check

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Speaker 1: digit for error detection. The stripe on the back of

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Speaker 1: the credit card is a magnetic stripe, often called a

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Speaker 1: mag stripe. The mag stripe is made up of tiny

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Speaker 1: iron based magnetic particles in a plastic like film. Each

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Speaker 1: particle you could think of as a very tiny bar magnet,

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Speaker 1: about twenty millions of an inch long. The mag stripe

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Speaker 1: can be written because the tiny our magnets can be

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Speaker 1: magnetized in either a north or a south pole direction.

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Speaker 1: The mag stripe on the back of the card is

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Speaker 1: very similar to a short piece of cassette tape fastened

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Speaker 1: to the back of the card. Instead of motors moving

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Speaker 1: the tape so it can be read, your hand provides

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Speaker 1: the motion as you swipe the card through a reader

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Speaker 1: or inserted in a reader at a gas station pump.

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Speaker 1: There are three tracks on that mag stripe. Each track

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Speaker 1: is about a tenth of an inch or two millimeters wide.

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Speaker 1: The I S O I e C Standard seven eight

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Speaker 1: one one says what will be on those tracks, and

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Speaker 1: it specifies that the first track holds seventy nine six

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Speaker 1: bit plus parity bit read only characters, Track two holds

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Speaker 1: forty four bit plus parity bit characters, and track three

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Speaker 1: holds a hundred and seven four bit plus parity bit characters.

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Speaker 1: This means that the first track can have alphabetic letters

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Speaker 1: in it, while the others have only numbers in them.

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Speaker 1: Your credit card typically uses only tracks one and two.

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Speaker 1: Track three is a ReadWrite track that includes an encrypted pin,

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Speaker 1: country code, currency units, and things like that, but it's

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Speaker 1: usage isn't standardized among banks, so it can't be used

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Speaker 1: that well. The information on track one is contained in

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Speaker 1: two formats, A which is reserved for proprietary use to

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Speaker 1: the card issuer, and BE, which is standardized and includes

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Speaker 1: the primary account number up to nineteen characters, a country

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Speaker 1: code of three characters, a name in alphabetic characters from

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Speaker 1: two to twenty six characters long, and then an expiration

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Speaker 1: date or a separator four characters or one character. The

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Speaker 1: format of Track two can only contain numbers, and it

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Speaker 1: was developed by the banking industry as follows. The first

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Speaker 1: part of it is a primary account number up to

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Speaker 1: nineteen characters. The second part is a country code of

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Speaker 1: three characters, and then there's a expliration data or a

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Speaker 1: separator of four characters or one character. There are three

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Speaker 1: basic methods for determining if your card is going to

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Speaker 1: be able to pay for what you're charging. In the

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Speaker 1: first method, merchants with a few transactions each month do

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Speaker 1: voice authentication using a touch tone phone. They call up

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Speaker 1: the card company and they can talk to a human

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Speaker 1: being if they need to. The second method, which is

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Speaker 1: far more common, is electronic data capture or e d C,

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Speaker 1: using mag stripe card readers like you see in stores

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Speaker 1: today or on gas pumps. These terminals can either call

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Speaker 1: up individually using a modem, or they can send their

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Speaker 1: data to a computer system that does the checking, and

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Speaker 1: then there's virtual terminal on the Internet. If the card

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Speaker 1: reader isn't able to accept your card, it's either because

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Speaker 1: it can't read your card or because the card company

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Speaker 1: has rejected it. If it can't read your card, it

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Speaker 1: could be because of a dirty or scratched mag stripe, or,

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Speaker 1: more likely, an erased bag stripe. The most common causes

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Speaker 1: for erased bag stripes are exposures to magnets like the

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Speaker 1: small ones used to hold notes and pictures on the refrigerator,

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Speaker 1: or exposure to r f I D readers. Do you

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Speaker 1: have any ideas or suggestions for this podcast? If so,

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Speaker 1: please send me an email at podcast at how stuff

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Speaker 1: works dot com. For more on this and thousands of

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Speaker 1: other topics, go to how stuff works dot com and

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