[citation needed] SD was designed to compete with the Memory Stick, a flash storage format with DRM Sony had released the year before.

[9] The trademarked SD logo was originally developed for the Super Density Disc, which was the unsuccessful Toshiba entry in the DVD format war.

The SD Association, which was headquartered in San Ramon, California, United States, then had 30 member companies and product manufacturers that made interoperable memory cards and devices.

[citation needed] MicroSD form-factor memory cards were introduced in 2004 by SanDisk at CeBIT[16] and originally called T-Flash,[17] and later TransFlash,[18] commonly abbreviated to "TF".

[citation needed] The storage density of memory cards increased significantly[quantify] throughout the 2010s, allowing the earliest devices to offer support for the SD:XC standard, such as the Samsung Galaxy S III and Samsung Galaxy Note II mobile phones, to expand their available storage to several hundreds of gigabytes.

In April 2024, Western Digital (SanDisk) revealed the world's first 4 TB SD card at NAB 2024, which will make use of the SDUC format.

Version 2.0 also introduces a high-speed bus mode for both SDSC and SDHC cards, which doubles the original Standard Speed clock to produce 25 MB/s.

[68][69][70][71] Version 4.0, introduced in June 2011, allows speeds of 156 MB/s to 312 MB/s over the four-lane (two differential lanes) UHS-II bus, which requires an additional row of physical pins.

[80] Users of older kernels or BSD can manually install third-party implementations of exFAT (as a FUSE module) in order to be able to mount exFAT-formatted volumes.

[81] However, SDXC cards can be reformatted to use any file system (such as ext4, UFS, VFAT or NTFS), alleviating the restrictions associated with exFAT availability.

The sequential performance aspect is the most relevant for storing and retrieving large files (relative to block sizes internal to the flash memory), such as images and multimedia.

The higher speed rates of UHS-II and III are achieved by using two-lane 0.4 V low-voltage differential signaling (LVDS) on a second row of pins.

[116] A2 class cards require host driver support as they use command queuing and write caching to achieve their higher speeds.

[117] In applications that require sustained write throughput, such as video recording, the device might not perform satisfactorily if the SD card's class rating falls below a particular speed.

Vendors have sought to differentiate their products in the market through various vendor-specific features: A SDIO (Secure Digital Input Output) card is an extension of the SD specification to cover I/O functions.

Two other unique features of Low-Speed SDIO are a maximum clock rate of 400 kHz for all communications, and the use of Pin 8 as "interrupt" to try to initiate dialogue with the host device.

[149] Host devices that comply with newer versions of the specification provide backward compatibility and accept older SD cards.

Due to the technical development of memory cards, users of existing mobile devices are able to expand their storage further and priceworthier with time.

They may also not present the best choice for applications that require higher storage capacities or speeds as provided by other flash card standards such as CompactFlash.

[b][154] Many personal computers of all types, including tablets and mobile phones, use SD cards, either through built-in slots or through an active electronic adapter.

Commonly found on the market are mislabeled or counterfeit Secure Digital cards that report a fake capacity or run slower than labeled.

[155][156][157] Software tools exist to check and detect counterfeit products,[158][159][160] and in some cases it is possible to repair these devices to remove the false capacity information and use its real storage limit.

The latter approach leverages the fact that counterfeited cards let the user read back files, which then consist of easily compressible uniform data (for example, repeating 0xFFs).

If not, SPI can also be emulated by bit banging (e.g. a SD card slot soldered to a Linksys WRT54G-TM router and wired to GPIO pins using DD-WRT's Linux kernel achieved only 1.6 Mbit/s throughput).

Universal support for FAT12, FAT16, FAT16B and FAT32 allows the use of SDSC and SDHC cards on most host computers with a compatible SD reader, to present the user with the familiar method of named files in a hierarchical directory tree.

In version 1 of the SD specification, capacities up to 2 GB[d] are calculated by combining fields of the CSD as follows: Later versions state (at Section 4.3.2) that a 2 GB SDSC card shall set its READ_BL_LEN (and WRITE_BL_LEN) to indicate 1,024 bytes, so that the above computation correctly reports the card's capacity, but that, for consistency, the host device shall not request (by CMD16) block lengths over 512 B.

[98] In the definition of SDHC cards in version 2.0, the C_SIZE portion of the CSD is 22 bits and it indicates the memory size in multiples of 512 KB (the C_SIZE_MULT field is removed and READ_BL_LEN is no longer used to compute capacity).

Subsequent to the release of most open-source drivers, the SDA provided a simplified version of the specification under a less restrictive license helping reduce some incompatibility issues.

[citation needed] Desktop card readers are themselves embedded systems; their manufacturers have usually paid the SDA for complete access to the SD specifications.

[citation needed] A malfunctioning SD card can be repaired using specialized equipment, as long as the middle part, containing the flash storage, is not physically damaged.