Editing SD card (section)

==Openness of specification==
{{More citations needed|section|date=September 2023}}
[[File:MicroSD to SD adapter, disassembled.png|thumb|Dismantled microSD to SD adapter showing the passive connection from the microSD card slot on the bottom to the SD pins on the top]]
Like most memory card formats, SD is covered by numerous [[patent]]s and [[trademark]]s. Excluding [[Secure Digital#SDIO cards|SDIO]] cards, [[Royalty payment|royalties]] for SD card licenses are imposed for manufacture and sale of memory cards and host adapters (US$1,000/year plus membership at US$1,500/year){{citation needed|date=September 2023}}

Early versions of the SD specification were available under a [[non-disclosure agreement]] (NDA) prohibiting development of [[open-source software|open-source]] drivers. However, the system was eventually [[reverse-engineered]] and free software drivers provided access to SD cards not using DRM. 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.<ref>{{cite web |url=http://www.linux.com/archive/feed/20060 |title=Sharp Linux PDA promotes the use of proprietary SD card, but more open MMC works just fine |date=14 June 2007 |publisher=Linux.com |access-date=2010-08-22 |archive-date=2010-12-15 |archive-url=https://web.archive.org/web/20101215172756/http://www.linux.com/archive/feed/20060 |url-status=live }}</ref>

Under a disclaimers agreement, the simplified specification released by the SDA in 2006 – as opposed to that of SD cards – was later extended to the physical layer, ASSD extensions, SDIO and SDIO [[Bluetooth]] Type-A.<ref>[http://www.sdcard.org/developers/tech/sdcard/pls/ Simplified Specification Agreement] {{webarchive |url=https://web.archive.org/web/20081028165644/http://www.sdcard.org/developers/tech/sdcard/pls/ |date=2008-10-28}} from the SDA's website</ref>

The Simplified Specification<ref>{{Cite web |url=https://www.taterli.com/wp-content/uploads/2017/05/Physical-Layer-Simplified-SpecificationV6.0.pdf |title=Simplified Specification|accessdate=July 31, 2024 |archive-date=December 18, 2020|archive-url=https://web.archive.org/web/20201218104400/https://www.taterli.com/wp-content/uploads/2017/05/Physical-Layer-Simplified-SpecificationV6.0.pdf |url-status=live}}</ref> is available.

Again, most of the information had already been discovered and [[Linux]] had a fully free driver for it. Still, building a chip conforming to this specification caused the [[One Laptop per Child]] project to claim "the first truly Open Source SD implementation, with no need to obtain an SDI license or sign NDAs to create SD drivers or applications."<ref>{{cite web|url=http://mailman.laptop.org/pipermail/community-news/2006-September/000023.html |title=OLPC mailing list archive |publisher=Mailman.laptop.org |access-date=2010-08-22 |archive-url=https://web.archive.org/web/20110412094819/http://mailman.laptop.org/pipermail/community-news/2006-September/000023.html |archive-date=2011-04-12}}</ref>

The proprietary nature of the complete SD specification affects [[embedded system]]s, laptop computers and some desktop computers; many desktop computers do not have card slots, instead using [[USB]]-based [[card reader#Memory card readers|card readers]] if necessary.{{citation needed|date=September 2023}} These card readers present a standard [[USB mass storage]] interface to memory cards, thus separating the operating system from the details of the underlying SD interface.{{citation needed|date=September 2023}} However, embedded systems (such as portable music players) usually gain direct access to SD cards and thus need complete programming information.{{citation needed|date=September 2023}} Desktop card readers are themselves embedded systems; their manufacturers have usually paid the SDA for complete access to the SD specifications.{{citation needed|date=September 2023}} Many notebook computers now include SD card readers not based on USB; device drivers for these essentially gain direct access to the SD card, as do embedded systems.{{citation needed|date=September 2023}}

The [[Serial Peripheral Interface Bus|SPI]]-bus interface mode is the only type that does not require a host license for accessing SD cards.{{citation needed|date=September 2023}}

[[File:Flash memory cards size.jpg|thumb|Size comparison of various flash cards: SD, [[CompactFlash]], [[MultiMediaCard|MMC]], [[xD-Picture Card|xD]]]]