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Alonso Tretyakov
Alonso Tretyakov


The standard was introduced in August 1999 by joint efforts between SanDisk, Panasonic (Matsushita) and Toshiba as an improvement over MultiMediaCards (MMCs),[1] and has become the industry standard. The three companies formed SD-3C, LLC, a company that licenses and enforces intellectual property rights associated with SD memory cards and SD host and ancillary products.[2]


In 1999, SanDisk, Panasonic (Matsushita), and Toshiba agreed to develop and market the Secure Digital (SD) Memory Card.[5] The card was derived from the MultiMediaCard (MMC) and provided digital rights management based on the Secure Digital Music Initiative (SDMI) standard and for the time, a high memory density.

At the 2000 Consumer Electronics Show (CES) trade show, the three companies announced the creation of the SD Association (SDA) to promote SD cards. The SD Association, headquartered in San Ramon, California, United States, started with about 30 companies and today consists of about 1,000 product manufacturers that make interoperable memory cards and devices. Early samples of the SD card[7] became available in the first quarter of 2000, with production quantities of 32 and 64 MB[8] cards available three months later.

The miniSD form was introduced at March 2003 CeBIT by SanDisk Corporation which announced and demonstrated it.[9] The SDA adopted the miniSD card in 2003 as a small form factor extension to the SD card standard. While the new cards were designed especially for mobile phones, they are usually packaged with a miniSD adapter that provides compatibility with a standard SD memory card slot.

The microSD removable miniaturized Secure Digital flash memory cards were originally named T-Flash or TF, abbreviations of TransFlash. TransFlash and microSD cards are functionally identical allowing either to operate in devices made for the other.[10] microSD (and TransFlash) cards are electrically compatible with larger SD cards and can be used in devices that accept SD cards with the help of a passive adapter, which contains no electronic components, only metal traces connecting the two sets of contacts. Unlike the larger SD cards, microSD does not offer a mechanical write protect switch, thus an operating-system-independent way of write protecting them does not exist in the general case. SanDisk conceived microSD when its Chief Technology Officer (CTO) and the CTO of Motorola concluded that current memory cards were too large for mobile phones.[citation needed]

The card was originally called T-Flash,[11] but just before product launch, T-Mobile sent a cease-and-desist letter to SanDisk claiming that T-Mobile owned the trademark on T-(anything),[citation needed] and the name was changed to TransFlash.

At CTIA Wireless 2005, the SDA announced the small microSD form factor along with SDHC secure digital high capacity formatting in excess of 2 GB[12] with a minimum sustained read and write speed of 17.6 Mbit/s.[13][citation needed] SanDisk induced the SDA to administer the microSD standard. The SDA approved the final microSD specification on July 13, 2005. Initially, microSD cards were available in capacities of 32, 64, and 128 MB.[citation needed]

The SDHC format, announced in January 2006, brought improvements such as 32 GB storage capacity[14] and mandatory support for FAT32 file system.[citation needed] In April, the SDA released a detailed specification for the non-security related parts of the SD memory card standard and for the Secure Digital Input Output (SDIO) cards and the standard SD host controller.[citation needed]

In September 2006, SanDisk announced the 4 GB miniSDHC.[15] Like the SD and SDHC, the miniSDHC card has the same form factor as the older miniSD card but the HC card requires HC support built into the host device. Devices that support miniSDHC work with miniSD and miniSDHC, but devices without specific support for miniSDHC work only with the older miniSD card. Since 2008, miniSD cards are no longer produced, due to market domination of the even smaller microSD cards.

The storage density of memory cards has increased significantly throughout the 2010s decade, 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 early 2011, Centon Electronics, Inc. (64 GB and 128 GB) and Lexar (128 GB) began shipping SDXC cards rated at Speed Class 10.[28] Pretec offered cards from 8 GB to 128 GB rated at Speed Class 16.[29] In September 2011, SanDisk released a 64 GB microSDXC card.[30] Kingmax released a comparable product in 2011.[31]

In April 2012, Panasonic introduced MicroP2 card format for professional video applications. The cards are essentially full-size SDHC or SDXC UHS-II cards, rated at UHS Speed Class U1.[32][33] An adapter allows MicroP2 cards to work in current P2 card equipment.[34]

Panasonic MicroP2 cards shipped in March 2013 and were the first UHS-II compliant products on market; initial offer includes a 32GB SDHC card and a 64GB SDXC card.[32][35] Later that year, Lexar released the first 256 GB SDXC card, based on 20 nm NAND flash technology.[36]

In February 2014, SanDisk introduced the first 128 GB microSDXC card,[37] which was followed by a 200 GB microSDXC card in March 2015.[38] September 2014 saw SanDisk announce the first 512 GB SDXC card.[39]

Samsung announced the world's first EVO Plus 256 GB microSDXC card in May 2016,[40] and in September 2016 Western Digital (SanDisk) announced that a prototype of the first 1 TB[41] SDXC card would be demonstrated at Photokina.[42]

In January 2018, Integral Memory unveiled its 512 GB microSDXC card.[44] In May 2018, PNY launched a 512 GB microSDXC card. In June 2018 Kingston announced its Canvas series of MicroSD cards which were capable of capacities up to 512 GB,[12] in three variations, Select, Go!, and React.[45]

Secure Digital includes five card families available in three sizes. The five families are the original Standard-Capacity (SDSC), the High-Capacity (SDHC), the eXtended-Capacity (SDXC), the Ultra-Capacity (SDUC) and the SDIO, which combines input/output functions with data storage.[47][48][49] The three form factors are the original size, the mini size, and the micro size. Electrically passive adapters allow a smaller card to fit and function in a device built for a larger card. The SD card's small footprint is an ideal storage medium for smaller, thinner, and more portable electronic devices.

The second-generation Secure Digital (SDSC or Secure Digital Standard Capacity) card was developed to improve on the MultiMediaCard (MMC) standard, which continued to evolve, but in a different direction. Secure Digital changed the MMC design in several ways:

The Secure Digital High Capacity (SDHC) format, announced in January 2006 and defined in version 2.0 of the SD specification, supports cards with capacities up to 32 GB.[12][47] The SDHC trademark is licensed to ensure compatibility.[50]

SDHC cards are physically and electrically identical to standard-capacity SD cards (SDSC). The major compatibility issues between SDHC and SDSC cards are the redefinition of the Card-Specific Data (CSD) register in version 2.0 (see below), and the fact that SDHC cards are shipped preformatted with the FAT32 file system.

SDHC host devices are required to accept older SD cards.[52] However, older host devices do not recognize SDHC or SDXC memory cards, although some devices can do so through a firmware upgrade.[53][better source needed] Older Windows operating systems released before Windows 7 require patches or service packs to support access to SDHC cards.[54][55][56]

The Secure Digital eXtended Capacity (SDXC) format, announced in January 2009 and defined in version 3.01 of the SD specification, supports cards up to 2 TB,[16] compared to a limit of 32 GB[12] for SDHC cards in the SD 2.0 specification. SDXC adopts Microsoft's exFAT file system as a mandatory feature.[57]

Version 3.01 also introduced the Ultra High Speed (UHS) bus for both SDHC and SDXC cards, with interface speeds from 50 MB/s to 104 MB/s for four-bit UHS-I bus.[58] (this number has since been exceeded with SanDisk proprietary technology for 170 MB/s read, which is not proprietary anymore, as Lexar has the 1066x running at 160 MB/s read and 120 MB/s write via UHS 1, and Kingston also has their Canvas Go! Plus, also running at 170 MB/s).[59][60][61][62]

Version 5.0 was announced in February 2016 at CP+ 2016, and added "Video Speed Class" ratings for UHS cards to handle higher resolution video formats like 8K.[63][64] The new ratings define a minimal write speed of 90 MB/s.[65][66]

The Secure Digital Ultra Capacity (SDUC) format, described in the SD 7.0 specification, and announced in June 2018, supports cards up to 128 TB[16] and offers speeds up to 985 MB/s, regardless of form factor, either micro or full size, or interface type including UHS-I, UHS-II, UHS-III or SD Express.[67] The SD Express interface can also be used with SDHC and SDXC cards.

SDXC and SDUC cards are normally formatted using the exFAT file system, thereby limiting their use to a limited set of operating systems. Therefore, exFAT-formatted SDXC cards are not a 100% universally readable exchange medium.

Windows Vista (SP1) and later[68] and OS X (10.6.5 and later) have native support for exFAT.[69][70] (Windows XP and Server 2003 can support exFAT via an optional update from Microsoft.)[71]Most BSD and Linux distributions did not, for legal reasons; though in Linux kernel 5.4 Microsoft open-sourced the spec and allowed the inclusion of an exFAT driver.[72] 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.[73] However, SDXC cards can be reformatted to use any file system (such as ext4, UFS, or VFAT), alleviating the restrictions associated with exFAT availability. 041b061a72


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