This is the more modern version of the Speed Class, with virtually all existing SD cards fitting into one of two UHS Speed Classes — either U1 or U3. These are denoted by either the number 1 or the number 3 within the letter “U” — usually found somewhere near the Speed Class. Most cards are going to be U3, which indicates a minimum write speed of 30 MB/s. Video Speed Class

SD Specifications Version 4.10", 3.10.5 – Summary of Bus Speed Mode for UHS-II Card (PDF), SD Association Kingston. "Kingston Digital Announces New 'Canvas' Series of Flash Cards". Kingston Technology Europe Co LLP . Retrieved 2018-11-19. Counterfeits [ edit ] Samsung Pro 64GB microSDXC original (left) and counterfeit (right): The counterfeit claims to have 64GB in capacity, but only 8GB (Class 4 speed) are usable: When trying to write more than 8 GB, data loss occurs. Also used for SanDisk 64GB fakes. Images of genuine, questionable, and counterfeit microSD (Secure Digital) cards before and after decapsulation. Details at source, photo by Andrew Huang.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 2TB, [b] compared to a limit of 32GB [d] for SDHC cards in the SD 2.0 specification. SDXC adopts Microsoft's exFAT file system as a mandatory feature. [53]

As an evolution of the XQD format, CFexpress is one of the best memory card formats around. However, it's currently only available with a limited number of high end cameras (mostly from Canon, Nikon and Panasonic). However, it's worth noting that the release of the Sony A7S III brought a somewhat confusing split into two different variants of CFexpress cards. Up until this point, all CFexpress-compatible cameras used CFexpress Type B cards (yes, 'B' does come before 'A' in this case!). Meanwhile, CFexpress Type A cards are smaller and slower. Crucially, Type B and Type A cards aren't interchangeable, so a camera such as the Nikon Z7 won't be able to accept a CFexpress Type A card. Vendors have sought to differentiate their products in the market through various vendor-specific features: Samsung announced the world's first EVO Plus 256GB microSDXC card in May 2016, [36] and in September 2016 Western Digital (SanDisk) announced that a prototype of the first 1 TB [c] SDXC card would be demonstrated at Photokina. [37]SanDisk. "SANDISK INTRODUCES WORLD'S HIGHEST CAPACITY microSDXC MEMORY CARD AT 128GB". www.sandisk.com. 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 SDXC specification mandates the use of Microsoft's proprietary exFAT file system, [160] which sometimes requires appropriate drivers (e.g. exfat-utils/ exfat-fuse on Linux). Activating New Mobile Services and Business Models with smartSD Memory cards" (PDF). SD Association. November 2014. Archived from the original (PDF) on 2016-12-23 . Retrieved 2017-08-02. CFexpress cards are typically also more durable than SD cards. More importantly, they’re a great feature for those who shoot video; now that high-bitrate (even RAW in some cases) 4K and 8K video is becoming commonplace, the CFexpress standard is the best option to make the most of that data. CFexpress Type C Two differential lines SD UHS-II mode: Uses two low-voltage differential signalling interfaces to transfer commands and data. UHS-II cards include this interface in addition to the SD bus modes. DeviceFidelity launches new range of NFC microSD devices". NFC World+. 2012-10-31 . Retrieved 2016-02-23.Interface [ edit ] Inside a 512MB SD card: NAND flash chip that holds the data (bottom) and SD controller (top) Inside a 2GB SD card: two NAND flash chips (top and middle), SD controller chip (bottom) Inside a 16GB SDHC card Command interface [ edit ] The command interface is an extension of the MultiMediaCard (MMC) interface. SD cards dropped support for some of the commands in the MMC protocol, but added commands related to copy protection. By using only commands supported by both standards until determining the type of card inserted, a host device can accommodate both SD and MMC cards. Cards that comply with UHS show Roman numerals 'I', 'II' or 'III' next to the SD card logo, [80] [78] and report this capability to the host device. Use of UHS-I requires that the host device command the card to drop from 3.3-volt to 1.8-volt operation over the I/O interface pins and select the four-bit transfer mode, while UHS-II requires 0.4-volt operation.

SD Standards Brochure 2017" (PDF). Archived from the original (PDF) on 2017-03-30 . Retrieved 2017-03-29.Panasonic Introduces New 64GB* and 48GB* SDXC Memory Cards, Available Globally in February 2010". Panasonic. Archived from the original on 2010-04-21 . Retrieved 2010-08-09. There is a proprietary UHS-I extension, called DDR200, originally created by SanDisk that increases transfer speed further to 170MB/s. Unlike UHS-II, it does not use additional pins. It achieves this by using the 208MHz frequency of the standard SDR104 mode, but using DDR transfers. [85] [86] This extension has since then been used by Lexar for their 1066x series (160MB/s), Kingston Canvas Go Plus (170MB/s) and the MyMemory PRO SD card (180MB/s).