There are three tracks on the magstripe. Each track is .110-inch wide. The ISO/IEC standard 7811, which is used bybanks, specifies:
- Track one is 210 bits per inch (bpi), and holds 79 six-bit plus parity bit read-only characters.
- Track two is 75 bpi, and holds 40 four-bit plus parity bit characters.
- Track three is 210 bpi, and holds 107 four-bit plus parity bit characters.
Yourcredit cardtypically uses only tracks one and two. Track three is a read/write track (that includes an encrypted PIN, country code,currencyunits, amount authorized), but its usage is not standardized among banks.
The information on track one is contained in two formats -- A, which is reserved for proprietary use of the card issuer, and B, which includes the following:
- Start sentinel -- 1 character
- Format code="B" -- 1 character (alpha only)
- Primary account number -- up to 19 characters
- Separator -- 1 character
- Country code -- 3 characters
- Name -- 2-26 characters
- Separator -- 1 character
- Expiration date or separator -- 4 characters or 1 character
- Discretionary data -- enough characters to fill out maximum record length (79 characters total)
- End sentinel -- 1 character
- Longitudinal Redundancy Check (LRC), a form of computed check character -- 1 character
The format for track two, developed by the banking industry, is as follows:
- Start sentinel -- 1 character
- Primary account number - up to 19 characters
- Separator -- 1 character
- Country code -- 3 characters
- Expiration date or separator -- 4 characters or 1 character
- Discretionary data -- enough characters to fill out maximum record length (40 characters total)
- LRC -- 1 character
There are three basic methods for determining that your credit card will pay for what you're charging:
- Merchants with few transactions each month dovoice authentication, using a touch tone phone.
- Electronic data capture (EDC)超级条码卡刷卡终端越来越common -- so is having you swipe your own card at the checkout.
- Virtual terminal on the Internet
This is how it works: After you or the cashier swipes your credit card through a reader, the EDC software at the point of sale (POS) terminal dials a stored telephone number via a modem to call anacquirer. An acquirer is an organization that collects credit authentication requests from merchants and provides a payment guarantee to the merchant.
When the acquirer company gets the credit card authentication request, it checks the transaction for validity and the record on the magstripe for:
- Merchant ID
- 有效的信用卡号码
- Expiration date
- Credit card limit
- Card usage
Single dial-up transactions are processed at 1200-2400 bps, while direct Internet attachment uses much higher speeds via this protocol. In this system, the cardholder enters apersonal identification number (PIN), using a keypad.
If the ATM isn't accepting your card, your problem is probably either:
- Dirty or scratched magstripe
- Erased magstripe (The most common causes for erased magstripes are exposure to magnets, like the small ones used to hold notes and pictures on the refrigerator, and a store's electronic article surveillance (EAS) tag demagnetizer.)