Editing SD card (section)

=== SD (SDSC) ===
{{More citations needed|section|date=September 2023}}

The original Secure Digital card, also known as Secure Digital Standard Capacity (SDSC), was developed as a second-generation successor to the [[MultiMediaCard]] (MMC) standard. While both formats continued to evolve, they diverged significantly in design and functionality. Secure Digital introduced several key changes to improve usability, durability, and performance:
* Asymmetrical shape of the sides of the SD card prevents inserting it upside down (whereas an MMC goes in most of the way but makes no contact if inverted).{{citation needed|date=September 2023}}
* Most standard size SD cards are {{Convert|2.1|mm|abbr=in}}<ref name="CS">{{Cite web |date=2020-12-11 |title=Capacity (SD/SDHC/SDXC/SDUC) {{!}} SD Association |url=https://www.sdcard.org/developers/sd-standard-overview/capacity-sd-sdhc-sdxc-sduc/ |access-date=2023-05-03 |website=sdcard.org |language=en-US |archive-date=2024-09-11 |archive-url=https://web.archive.org/web/20240911012954/https://www.sdcard.org/developers/sd-standard-overview/capacity-sd-sdhc-sdxc-sduc/ |url-status=live}}</ref> thick, with microSD versions being {{Convert|1.0|mm|abbr=in}}<ref name="CS" /> thick, compared to {{Convert|1.4|mm|abbr=in}} for MMCs. The SD specification defines a card called '''Thin SD''' with a thickness of 1.4&nbsp;mm,<ref name=":0">{{Cite book |url=https://www.sdcard.org/downloads/pls/pdf/?p=Part1_Physical_Layer_Simplified_Specification_Ver9.10.jpg&f=Part1PhysicalLayerSimplifiedSpecificationVer9.10Fin_20231201.pdf&e=EN_SS9_1 |title=SD Specifications Part 1 Physical Layer Simplified Specification |date=December 1, 2023 |publisher=SD Card Association |edition=9.10 |page=5}}</ref> however it was rarely used, as the SDA went on to define even smaller form factors.
* The card's electrical contacts are recessed beneath the surface of the card, protecting them from contact with a user's fingers.
* The SD specification envisioned capacities and transfer rates exceeding those of MMC, and both of these functionalities have grown over time.{{citation needed|date=September 2023}} For a comparison table, see [[#Comparison to other flash memory formats|below]].
* While MMC uses a single pin for data transfers, the SD card added a four-wire bus mode for higher data rates.{{citation needed|date=September 2023}}
* The SD card added [[Content Protection for Recordable Media]] (CPRM) security circuitry for [[digital rights management]] (DRM) content-protection, although it is rarely used and most devices don't support it.<ref>{{Cite web |title=Definition of CPRM |url=https://www.pcmag.com/encyclopedia/term/cprm |access-date=2025-04-29 |website=PCMAG |language=en |archive-date=29 April 2025 |archive-url=https://web.archive.org/web/20250429025631/https://www.pcmag.com/encyclopedia/term/cprm |url-status=live }}</ref><ref>{{Cite web |title=Copyright Protection for Digital Data (CPRM) |url=https://www.sdcard.org/consumers/about-sd-memory-card-choices/copyright-protection-for-digital-data-cprm/ |access-date=2025-04-29 |website=SD Association |language=en-US |archive-date=29 April 2025 |archive-url=https://web.archive.org/web/20250429025631/https://www.sdcard.org/consumers/about-sd-memory-card-choices/copyright-protection-for-digital-data-cprm/ |url-status=live }}</ref>
* Addition of a write-protect notch{{citation needed|date=September 2023}}

The official SDSC specification supports card sizes up to 2 GB and uses a logo to distinguish it from later SD formats.

Due to physical differences, full-size SD cards are incompatible with slimmer MMC slots, and other electrical and protocol-level differences further limit interoperability between the two formats.{{citation needed|date=September 2023}}