A credit card is a thin plastic card, usually 3-1/8 inches by 2-1/8 inches in size, that contains identification information such as a signature or picture, and authorizes the person named on it to charge purchases or services to his account -- charges for which he will be billed periodically. Today, the information on the card is read by automated teller machines (ATMs), store readers, and bank and Internet computers.
The magstripe from the credit card can be "written" because the tiny bar magnets can be magnetized in either a north or south pole direction. The magstripe on the back of the card is very similar to a piece of cassette tape.
There are three tracks on the magstripe. Each track is about one-tenth of an inch wide. 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 - one character
- Format code="B" - one character (alpha only)
- Primary account number - up to 19 characters
- Separator - one character
- Country code - three characters
- Name - two to 26 characters
- Separator - one character
- Expiration date or separator - four characters or one character
- Discretionary data - enough characters to fill out maximum record length (79 characters tota)
- End sentinel - one character
- Longitudinal redundancy check (LRC) - one character
- LRC is a form of computed check character.
The format for track two, developed by the banking industry, is as follows:
- Start sentinel - one character
- Primary account number - up to 19 characters
- Separator - one character
- Country code - three characters
- Expiration date or separator - four characters or one character
- Discretionary data - enough characters to fill out maximum record length
- LRC - one character
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