SDkaardiliides

SDkaardiliides, or the SD card interface, is the standard that defines how Secure Digital cards connect to hosts such as cameras, phones, laptops, and embedded devices. It specifies the electrical signaling, data transfer protocols, and command structure that enable the host to read and write data on the card. The standard is developed and maintained by the SD Association, a group founded by SanDisk, Panasonic (Matsushita), and Toshiba.

The interface encompasses several card formats (SD, SDHC, SDXC, SDUC and microSD variants), multiple operation modes (SD mode and the SPI mode), and both 1-bit and 4-bit data transfer. In SD mode, data transfers use dedicated data lines and a set of commands; in SPI mode, a simplified serial bus is used, compatible with more general microcontroller systems.

The SD interface has evolved through several performance tiers, including High Speed, Ultra High Speed (UHS), and more recently SD Express, which uses PCIe or NVMe signaling to reach higher transfer rates. Card capacity has expanded across generations: standard SD, SDHC, SDXC, and SDUC. The interface also supports features such as card detection, read and write protections, and error correction.

Practical use: the SD card interface is ubiquitous in consumer electronics for removable storage, enabling hot-swapping, plug-and-play operation, and broad interoperability between devices and operating systems. It remains the basis for many embedded storage solutions and continues to be developed by the SD Association.