The first few digits of a credit card number play an important role in revealing the issuing organization to which the card belongs. Those starting with 6 represent UnionPay cards, those starting with 4 are Visa cards, those starting with 5 are Mastercard cards, and those starting with 3 have the JCB logo. The first six digits of the card number are called the BIN code, which is the bank's identification code and is assigned to various banking institutions by the International Organization for Standardization.

BIN consists of six digits and is used to distinguish different card issuers. The entire card number consists of the card issuer's identification code, custom digits and verification code. This information together constitutes the cardholder's identity. In China, bank cards are mainly distinguished according to the first number. For example, those starting with 4 belong to VISA, those starting with 5 belong to Mastercard, and those starting with 9, 62, and 60 are China UnionPay cards, among which UnionPay cards starting with 62 and 60 Comply with international standards and universally applicable.

The most commonly seen credit card length is 16 digits, such as American Express card, which is 15 digits in length, including information about the brand, organization and card-issuing branch. For example, in the 16-digit card number of Bank of Communications credit card, the first six digits represent the card organization: 4 at the beginning is VISA, 5 is Mastercard, and 6 is UnionPay single currency card. The detailed BIN numbers of various Bank of Communications credit cards are such as VISA regular card 458123, Master regular card 521899, etc. Different card types have different following digits.

In general, the first digits of a credit card number are the key to identifying the card type and card issuer, and help to understand its scope of use and characteristics.