The Secure Digital Association is the industry group that publishes the specification for the small removable memory card used in phones, cameras, and other devices. Members build cards and the slots that read them. The association publishes the sizes, the electrical interface, and the file-system rules.
The card itself is Secure Digital (SD). The association is the body that writes the specification. A card that follows the specification can be read by a slot built to the same document.
What the Specification Fixes
- Sizes. The full-size card, the mini card, and the micro card.
- Capacity classes. How much data a card of a given class is specified to hold.
- The host interface. How a device talks to the card and how the card answers.
The Association and a Card Maker
| Compared | The Association | A Card Maker |
| Writes the specification | Yes | Builds to it |
| Sells a card | No | Yes |
| A new capacity | Added to the specification | Ships a card once the spec allows it |