Editing SD card (section)

=== {{Anchor|Ultra High Speed|UHS}} UHS (Ultra High Speed) ===

The '''Ultra High Speed''' ('''UHS''') bus is a type of interface used by some [[Secure Digital#SDHC|SDHC]] and [[Secure Digital#SDXC|SDXC]] cards to enable faster data transfer between the card and a host device.<ref name="sda_bus_speed">{{cite web |url=https://www.sdcard.org/developers/overview/bus_speed/ |title=Bus Speed (Default Speed/ High Speed/ UHS) |publisher=SD Association |access-date=2013-11-13 |archive-date=2016-10-04 |archive-url=https://web.archive.org/web/20161004053633/https://www.sdcard.org/developers/overview/bus_speed/ |url-status=live }}</ref><ref>{{cite web |url=https://www.engadget.com/2010/06/24/sd-cards-branded-with-an-upper-case-i-are-faster-yo/ |title=SD cards branded with an upper-case 'I' are faster, yo |publisher=Engadget |date=2010-06-24 |access-date=2010-08-22 |archive-date=2010-08-28 |archive-url=https://web.archive.org/web/20100828145021/http://www.engadget.com/2010/06/24/sd-cards-branded-with-an-upper-case-i-are-faster-yo/ |url-status=live }}</ref>

UHS-compatible cards are marked with Roman numerals next to the SD logo, indicating the version of the UHS standard they support.<ref name="sda_bus_speed"/><ref name="sda_speed_class">{{cite web |title=SD Speed Class |url=https://www.sdcard.org/developers/overview/speed_class |url-status=dead |archive-url=https://web.archive.org/web/20201221172542/https://www.sdcard.org/developers/overview/speed_class/ |archive-date=2020-12-21 |access-date=2013-11-13 |publisher=SD Association}}</ref> These cards offer significantly faster read and write speeds than earlier SD card types, making them well suited for high-resolution video, burst photography, and other data-intensive applications.

To achieve higher transfer speeds, UHS cards and devices use specialized electrical signaling and hardware interfaces. UHS-I cards operate at 1.8&nbsp;V instead of the standard 3.3&nbsp;V and use a four-bit transfer mode. UHS-II and UHS-III introduce a second row of interface pins and use [[low-voltage differential signaling]] (LVDS) at 0.4&nbsp;V to increase speed and reduce power consumption and electromagnetic interference (EMI).<ref>{{cite web |title=SD Standard Overview |url=https://www.sdcard.org/developers/sd-standard-overview/ |website=SD Association |date=2020-12-11 |access-date=2023-06-19}}</ref>

Each LVDS lane can transfer up to 156&nbsp;MB/s. In full-duplex mode, one lane is used for sending data and the other for receiving. In half-duplex mode, both lanes operate in the same direction, effectively doubling the data rate at the same clock speed.

The following UHS speed classes are defined:

==== UHS-I ====

Support for the Ultra High Speed interface was first specified in SD version 3.01, released in May 2010.<ref name="SDHCspec">{{cite web |publisher=SD Association |url=http://www.sdcard.org/downloads/pls/simplified_specs/archive/part1_301.pdf |title=SD Part 1, Physical Layer Simplified Specification, Version 3.01 |date=2010-05-18 |access-date=2013-11-25 |archive-url=https://web.archive.org/web/20131205014133/https://www.sdcard.org/downloads/pls/simplified_specs/archive/part1_301.pdf |archive-date=2013-12-05 |url-status=dead }}</ref> This version introduced support for a 100&nbsp;MHz clock frequency—four times the rate of the original "Default Speed"—which enabled transfer rates up to 50&nbsp;MB/s using four-bit Single Data Rate (SDR) transfers, designated as '''SDR50'''. An extended mode called '''SDR104''' (also part of UHS-I) further increased the clock frequency to 208&nbsp;MHz, enabling data rates up to 104&nbsp;MB/s.

Version 3.01 also introduced '''DDR50''', a [[double data rate]] mode that transmits data on both the rising and falling edges of the clock signal. At 50&nbsp;MHz, DDR50 can achieve 50&nbsp;MB/s transfer rates by sending four bits per edge, or eight bits (one byte) per full clock cycle. This mode is mandatory for microSDHC and microSDXC cards labeled as UHS-I.

A proprietary extension of UHS-I, known as '''DDR200''', was developed by SanDisk to further increase transfer speeds without requiring additional pins. It combines double data rate transfers with the 208&nbsp;MHz clock of SDR104 to reach speeds of up to 170&nbsp;MB/s.<ref>{{cite web |title=SanDisk Extreme microSDXC datasheet |url=https://documents.westerndigital.com/content/dam/doc-library/en_us/assets/public/sandisk/product/memory-cards/extreme-uhs-i-microsd/data-sheet-extreme-uhs-i-microsd.pdf |website=Western Digital |access-date=2021-02-04 |archive-date=2021-01-08 |archive-url=https://web.archive.org/web/20210108210349/https://documents.westerndigital.com/content/dam/doc-library/en_us/assets/public/sandisk/product/memory-cards/extreme-uhs-i-microsd/data-sheet-extreme-uhs-i-microsd.pdf |url-status=live }}</ref><ref>{{cite web |title=GL3232 |url=http://www.genesyslogic.com/en/product_view.php?show=83 |website=Genesys Logic |access-date=2021-02-04 |archive-date=2020-09-21 |archive-url=https://web.archive.org/web/20200921071215/http://www.genesyslogic.com/en/product_view.php?show=83 |url-status=live }}</ref> Although not part of the official SD specification, DDR200 has been adopted by several manufacturers, including Lexar (1066x series, up to 160&nbsp;MB/s), Kingston (Canvas Go Plus, up to 170&nbsp;MB/s), and MyMemory (PRO SD card, up to 180&nbsp;MB/s).

==== UHS-II ====
[[File:Lexar 1000x MicroSDHC UHS-II U3 Class 10 - Back.jpg|thumb|upright|Back side of a Lexar UHS-II microSDHC card, showing the additional row of UHS-II connections]]

Specified in version 4.0, further raises the data transfer rate to a theoretical maximum of 156&nbsp;MB/s (full-[[Duplex (telecommunications)|duplex]]) or 312&nbsp;MB/s (half-duplex) using an additional row of pins for LVDS signalling<ref name="firstsdxc">{{cite web | url = https://www.sdcard.org/press/SD_Association_Announces_UHS-II_eBOOK_Jan_5_2011_ENGLISH.PDF | publisher = SD Card | title = Association Triples Speeds with UHS-II | date = 5 January 2011 | access-date = 2011-08-09 | archive-date = 2011-03-21 | archive-url = https://web.archive.org/web/20110321195143/http://www.sdcard.org/press/SD_Association_Announces_UHS-II_eBOOK_Jan_5_2011_ENGLISH.PDF | url-status = dead }}</ref> (a total of 17 pins for full-size and 16 pins for micro-size cards).<ref name="sda_bus_speed"/> While first implementations in compact system cameras were seen three years after specification (2014), it took many more years until UHS-II was implemented on a regular basis. At the beginning of 2025, 100 DSLR and mirrorless cameras support UHS-II.<ref>{{cite web |url=https://www.memorycard-lab.com/-Article/UHS-II-Cameras | publisher = memorycard-lab.com | title = UHS-II camera list | access-date=2025-01-04}}</ref>

==== UHS-III ====
Version 6.0, released in February 2017, added two new data rates to the standard. FD312 provides 312&nbsp;MB/s while FD624 doubles that. Both are full-duplex. The physical interface and pin-layout are the same as with UHS-II, retaining backward compatibility.<ref>{{Cite web|url=https://www.sdcard.org/press/DoublesTransferSpeeds_with_UHS3_2_9_2017.pdf|title=SD Association Doubles Bus Interface Speeds with UHS-III|date=23 February 2017|access-date=23 February 2017|archive-date=24 February 2017|archive-url=https://web.archive.org/web/20170224211349/https://www.sdcard.org/press/DoublesTransferSpeeds_with_UHS3_2_9_2017.pdf|url-status=dead}}</ref>