SD card Secure Digital
Removable flash memory card — standard since 1999, comes in the sub-formats SD, miniSD (extinct), microSD.
Capacity classes: SD (≤ 2 GB), SDHC (≤ 32 GB), SDXC (≤ 2 TB), SDUC (≤ 128 TB). Speed classes: Class 2/4/6/10, UHS-I (104 MB/s), UHS-II (312 MB/s, doubled pin row), UHS-III (624 MB/s), SD Express (PCIe NVMe, 4 GB/s). Video Speed Class V6–V90 guarantees minimum write speed for 4K/8K recording. Apple stopped using SD in iPhones (it has never had it); Samsung Galaxy dropped microSD support from the S21 onward. Competition: CFexpress (pro cameras), UFS cards (Huawei push).