Card format options are related to card numbering in two ways: the number of card numbers available and how card numbers are tracked.

26 bit format (also known as H10301) is the industry standard format and is the most commonly used. The range of card numbers available in 26 bit format is limited, and therefore, there is potential for the card numbers to be duplicated. The end user controls the card numbers of 26 bit cards, and the primary benefits of using this format are the convenience of ordering cards and universal access control panel acceptance.
37 bit format cards (also known as H10302) cards are also commonly used. HID controls card numbering of 37 bit cards, and assures that the numbers are unique and will not be duplicated. Before ordering 37 bit cards, confirm that your system is capable of using a 37 bit number with no facility code.
35 bit Corporate 1000 cards were designed to provide large end users with their own format, ensuring that card numbers are always unique and cannot be duplicated. The Corporate 1000 format also provides the end user security by authorizing only the dealer of their choice to be able to provide their card format, as well as the flexibility of controlling card numbering and issuance for their organization.
40 bit format cards (also known as C10106) are also commonly used cards and are compatible with Casi Rusco access control systems. Card numbers for C10106 cards are assigned by HID, which makes them very easy to order. This also means that there is no risk of duplication of card numbers.
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