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Canon 6D SD card slot

Canon 6D SD Card Comparison Test

Published: December 19, 2014

The Canon 6D offers a 20.2 megapixel full-frame sensor in a compact DSLR body size. Its DIGIC 5+ Image Processor enables up 4.5 frames per second continuous shooting. It supports Ultra High Speed (UHS-I) Secure Digital memory cards for fast write speed.

The following tests compare the performance of 32 high-speed SD cards in the Canon 6D and reveal the fastest card for this camera. Many SD cards claim a high transfer rate, but they are often only quoted with a read speed; the write speed may be significantly lower. Furthermore, write speed may be limited by the device or camera in which it is used, as is the case with the Canon 6D. Paying a premium price for a fast card may provide diminishing returns in this camera.

The most direct speed comparison uses write speed, a measurement of the rate the camera writes pictures to the card. This speed is most important during sustained burst shooting. Write speed results are dipslayed below in the write speed test. How the write speed impacts actual performance is shown in the continuous shooting test, a measurement of how many shots can be taken in 30 seconds using three different image settings. A detailed performance analysis explains some details found during testing and recommended SD cards for the 6D are provided based on the test results.

Camera Card Speed Test Details

  • Camera: Canon 6D
  • Test date: December 17, 2014
  • Firmware version: 1.1.4
  • Image file size in tests:
    • RAW: 28.5 MB
    • JPEG (Large, Fine): 10.4 MB
  • Each card formatted using "low-level format" in camera
  • Camera settings:
    • ISO 100
    • manual exposure
    • 1/60 shutter speed
    • custom white balance
    • standard picture style
    • auto lighting optimizer disabled
    • long exp. noise reduction off
    • high ISO speed NR off
    • highlight tone priority off
    • image review off
    • lens aberration correction disabled
    • continuous high shooting drive mode
    • WiFi disabled
    • GPS disabled

The camera is placed on a tripod and aimed at a detailed test scene with controlled lighting. Manual focus is set using Live View at 10X magnification. A timed remote shutter release provides consistent time intervals and minimizes camera movement throughout the tests. The write time is determined by reviewing a video of the card access light and is accurate to within a few hundredths of a second. The total number bytes written to the card divided by the write time equals the write speed in megabytes per second (1 MB = 1,048,576 bytes). Write speed is provided for RAW image format (RAW+JPEG and JPEG have lower write speeds).

Write Speed Test Results

Continuous Shooting Test

The Canon 6D burst shooting test measures the number of images taken in 30 seconds using three different image settings: RAW+JPEG, RAW, and JPEG. The JPEG setting is Large, Fine. It must be emphasized that the image subject affects the number of images that can be taken. Detailed subjects create large file sizes, which take longer to write and decrease the number of images that can be taken in a given time interval compared with simple subjects. This test creates average file sizes of 28.5MB RAW and 10.4MB JPEG. The test is optimized to show the difference in write speed between cards, rather than an optimistic value provided by a more simple image subject.

6D Performance Analysis

Canon 6D SD card slot

Although the Canon 6D supports UHS-I SD cards, its write speed is well below the theoretical maximum provided by UHS-I (104MB/s). In continuous shooting the 6D write speed topped out around 36MB/s. One interesting observation is the fastest 11 SD cards in this test were all SanDisk and Kingston. Samsung PRO and Toshiba Exceria Type 1 and Type 2 cards performed slower than expected in the 6D compared with their performance in other cameras. Samsung cards were notably slow during JPEG burst shooting.

The 6D is limited by a relatively small buffer and modest write speed. The largest difference between cards is observed after the buffer has filled, at which point further shooting is limited by the write speed of the memory card. Using our detailed test scene, the 6D could manage 7 frames RAW+JPEG, 13-15 RAW and 23-58 shots JPEG before the frame rate slowed. Faster cards were able to clear the buffer faster allowing more shots at full frame rate before the buffer reached its threshold. Continuing to shoot for the remainder of time after the buffer filled, the fastest card provided 1.3 fps, while the slowest card provided 0.6 fps in RAW mode. In JPEG with the buffer full, the range was 3.24 fps to to 1.5 fps. No card was able sustain more than 1 fps in RAW+JPEG mode after the buffer had filled.

The number of shots and frames per second in continuous shooting depend on camera settings as well as the scene. More detailed scenes create larger files and reduce the number of frames and frame rate in an extended burst shooting test. The actual numbers in continuous shooting (including "buffer capacity") vary with camera settings and different image subjects.

Recommended SD Cards for the Canon 6D

The fastest SD card for the Canon 6D is the SanDisk Extreme Pro 95MB/s UHS-I. Both the 64GB and 32GB cards tested provided the top write speed and greatest number of shots in 30 seconds. The Extreme Pro is capable of over 90MB/s write speed, but the 6D does not reach anywhere near the write speed potential of this card.

From a value perspective, SanDisk Extreme 60MB/s SD cards provide nearly the top performance in the 6D at a much more reasonable cost. Both 32 and 64 GB capacity cards performed nearly identically. The Kingston Class 10 UHS-I 64GB SDXC card provides great speed for its price and supports a faster read speed (97 MB/s in benchmark tests) compared with the Extreme 60MB/s. Other notable value cards for the Canon 6D include the Patriot EP Pro, Transcend 95/60 and PNY Elite Performance 64GB SDXC.

Downloading pictures from the Canon 6D

Canon 6D USB 3.0 cable connection to download files

The 6D has a built-in USB 2.0 port that can be used to download pictures from the camera. USB 2.0 connections are typically limited to 35MB/s, and the transfer speed measured in the 6D was slightly lower. Using the fastest SanDisk Extreme Pro 95MB/s UHS-I card in the 6D, the average transfer speed was 24.8MB/s downloading RAW images using a USB cable.

A separate USB 3.0 card reader can provide much faster transfers. The same SanDisk Extreme Pro card can provide around 90MB/s actual download speed copying RAW files to a computer. See the Card Reader Reviews for reviews and speed tests of several card readers.


Explore the

Sony announces new TOUGH SDHC UHS-II Memory Cards, the world’s toughest and fastest memory cards. Available in early October, the new TOUGH SD cards will feature durability and speed unseen in conventional SD cards, allowing photographers and filmmakers to fully focus on bring creative without worry.

The TOUGH SD cards feature the world’s first one-piece molded construction and rib-less design with No-Write Switch, making them far less vulnerable than conventional SD cards. In a bend test comparing the TOUGH SD cards to the standard, the TOUGH SD came out as 18 times stronger. These new cards also have the highest grade dustproof protection and are waterproof for up to 72 hours at a depth of 15 feet.

The cards boast an ultra-fast write speed of up to 299 MB/s – fast enough to support continuous shooting of high-resolution images and 4K video. When it comes to transferring those files to your computer, the cards’ read speeds of up to 300 MB/s makes the process take only seconds.

Before your card reaches its write cycle limit, the SD Scan Utility will let you know. It checks the health of the card by scanning its Flash memory, so you can always know the status of your TOUGH SD card.

The TOUGH memory cards will come in three different capacities in the SF-G range; 32GB, 64GB and 128GB. Check back to for more information on where to buy them. 

See full official press release below:

Sony Introduces the World’s Toughest and Fastest SD Card

— Completely Sealed one-piece Molded structure and Ribless, Switchless Design Keeps Images Safe and Guards against Drops, Bends, Water and Dust —

SAN DIEGO — August 28, 2018 — Sony’s new “SF-G series TOUGH specification” UHS-II SD cards are designed to keep images safe in any shooting environment, combining the world’s fastest read and write speeds with an ultra-rugged design that is bend-proof, drop-proof to 5 meters, water-proof and dust-proof.

The new cards are 18 times stronger than SD standard (180N compared to 10N rating) to guard against bending and dropping, and use the world’s first monolithic structure with a completely sealed one-piece molding that leaves no empty space in the card and prevents dust or debris from entering. The TOUGH spec. series uses materials of high-grade hardness, unlike conventional SD which uses a thin, 3-part ensemble. They are protected against typical physical damage that can affect conventional SD cards such as a broken plastic casing, broken data protection lock and broken connector ribs.

For photographers fighting the elements to get the perfect shot, the TOUGH spec. SD cards are also waterproof with an IPX8 rating and dustproof with an IP6X rating.

As the world’s first ribless SD card with no write protection switch, the new cards’ design ensures that easy-to-break parts are removed entirely.

Unleash the power of the camera

Continuing an industry trend driven by Sony, full-frame mirrorless cameras such as the α9 and α7 series are packing more and more performance into stills and video performance. These high-end cameras rely on fast memory cards to maximize their performance and with professional photographers now using SD cards more frequently, users are demanding higher levels of reliability and durability associated with other professional card types. With the world’s fastest write speed of up to 299MB/s, buffer clearing time is minimized, allowing photographers to shoot at the highest burst speeds.

The TOUGH spec. SD cards also support V90, the highest standard of video speed class, making it an ideal companion for shooting high-resolution video.

Transferring high-capacity photo and video files is made simple with the TOUGH spec. cards, thanks to a read speed of up to 300MB/s, another world’s fastest, which dramatically streamlines the post-shooting workflow. Addressing the practical needs of photographers, the SF-G series TOUGH specification range feature a bright yellow banding design, making the card easier to spot in dark shooting conditions.

Ultimate Assurance

The TOUGH spec. series SD cards include a SD Scan Utility, allowing the user to check that the card is in good condition and File Rescue Software to recover accidentally deleted data and photos. The new cards are also X-ray proof, magnet proof, anti-static, temperature proof and feature UV Guard.

Pricing and Availability

Full product details are available at: The new SF-G TOUGH series of memory cards are planned to be available in October, at the following suggested retail prices:

  • SF-G32T/T1 – 32GB - $72.99
  • SF-G64T/T1 – 64GB - $131.99
  • SF-G128T/T1 – 128GB -- $275.99
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SanDisk’s New Extreme Pro SD UHS-II Cards are World’s Fastest SD Cards


SanDisk has released new UHS-II SD cards with write speeds up to 250MB/s and read speeds up to 280MB/s. This new line gets its major speed boost from the UHS-II bus interface. Most SD-compatible cameras currently on the market support UHS-I, at best; however, we are just starting to see new cameras with UHS-II support (like the Fuji X-T1).

The new UHS-II bus interface offers the ability to build cards with up to 312MB/s transfer speeds, which is a big jump from the maximum theoretical speeds on the UHS-I interface at 104MB/s.

UHS-II Cards with Second Row of Pins

The new UHS-II cards have a second row of pins to support the higher data transfer rates. The first row of pins are identical to the standard SD cards we’ve seen on the market over the past several years and allow UHS-II cards to function normally in older, non-UHS II devices. Of course, if you don’t have a UHS-II compatible device, you will not see the speed benefits from the UHS-II bus interface.

UHS Speed Class symbols, such as U1 and U3, indicate minimum write speeds for real-time video recording. For UHS rated cards, you will find the numeric class rating within the letter “U” on the card’s label.  (See the U3 labeling in the top image.)

Compressed 4K video capture data transfer rates will vary among cameras depending on what codec the camera uses. The new U3 Speed Class should be plenty fast enough to handle Sony’s XAVC-S 4K codec (used in the new Sony FDR-AX1), which captures 4K video at a 150Mb/s data rate. The U3 Speed Class at 30MB/s minimum write speed translates to a 240Mb/s data rate. While the 30MB/s minimum write speed may seem low, it’s worth noting that the SD Association has not established a speed class rating higher than U3 at the time of this card’s release.

Photographers need to keep in mind that the U1 and U3 ratings are practically meaningless for still photography. The max data transfer rates can vary widely among cards with the same U1 and U3 ratings.

Additionally, while there are UHS-I cards that offer a U3 speed class rating, it is unclear whether the U3 rating on these new SanDisk cards is valid for non-UHS-II devices. For more about SD card types and ratings, see the resource article Demystifying SD Cards.

The new SanDisk Extreme PRO UHS-II cards should be available in April in 16GB to 64GB capacities for $119.99 to $299.99.

SanDisk UHS-II Card Reader

SanDisk UHS-II Card Reader

SanDisk also unveiled a new reader with UHS-II compatibility and USB 3.0 interface, which should also be available in April for $49.99.

Filed Under: GearTagged With: memory card, sandisk, sdhc, sdxc, Speed Class 3, U3, UHS-II

Choosing the Best SD Card for Video – Understanding All the Numbers and Symbols on SD Memory Cards

SD card

Type of memory storage for portable devices

"SDHC" redirects here. For the gene, see SDHC (gene).

SD Cards.svg

From top to bottom: SD, miniSD, microSD

Media typeMemory card
  • SD: Up to 2 GB
  • SDHC: over 2 GB to 32 GB
  • SDXC: over 32 GB to 2 TB
  • SDUC: over 2 TB to 128 TB
Block sizeVariable
Read mechanism
  • Standard: 12.5 MB/s
  • High-speed: 25 MB/s
  • UHS-I: 50 MB/s or 104 MB/s
  • UHS-II: 156 MB/s full-duplex, or 312 MB/s half-duplex
  • UHS-III: 312 MB/s full-duplex, or 624 MB/s half-duplex
  • Express: ≥ 985 MB/s full-duplex
Write mechanismSame as Read
StandardSD Standard
Developed bySD Association
  • Standard:
  • 32.0×24.0×2.1 mm (1.260×0.945×0.083 in), 1,612.8 mm3 (0.09842 in3)
  • Mini:
  • 21.5×20.0×1.4 mm (0.846×0.787×0.055 in), 602 mm3 (0.0367 in3)
  • Micro:
  • 15.0×11.0×1.0 mm (0.591×0.433×0.039 in), 165 mm3 (0.0101 in3)
  • Standard: ~2 g
  • Mini: ~800 mg
  • Micro: ~250 mg
UsagePortable devices, such as digital cameras and mobile phones (including most smartphones)
Extended fromMultiMediaCard
ReleasedAugust 1999

Secure Digital, officially abbreviated as SD, is a proprietarynon-volatilememory card format developed by the SD Association (SDA) for use in portable devices.

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]

The companies also formed the SD Association (SDA), a non-profit organization, in January 2000 to promote and create SD Card standards.[3] SDA today has about 1,000 member companies. The SDA uses several trademarkedlogos owned and licensed by SD-3C to enforce compliance with its specifications and assure users of compatibility.[4]


1999–2002: Creation[edit]

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.

It was designed to compete with the Memory Stick, a DRM product that Sony had released the year before. Developers predicted that DRM would induce wide use by music suppliers concerned about piracy.[6]

The trademarked "SD" logo was originally developed for the Super Density Disc, which was the unsuccessful Toshiba entry in the DVDformat war. For this reason the D within the logo resembles an optical disc.

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.

2003: Mini cards[edit]

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.

2004–2005: Micro cards[edit]

See also: § Mobile phones

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] 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 Motorola E398 was the first mobile phone to contain a TransFlash (later microSD) card.[citation needed] A few years later, its competitors began using microSD cards.

2006–2008: SDHC and SDIO[edit]

This microSDHC card holds 8 billion bytes. Beneath it is a section of a magnetic-core memory(used until the 1970s) that holds eight bytes using 64 cores. The card covers approximately 20 bits (2 1/2 bytes)

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.

2009–2018: SDXC[edit]

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 January 2009, the SDA announced the SDXC family, which supports cards up to 2 TB[16] and speeds up to 300 MB/s.[citation needed] SDXC cards are formatted with the exFAT filesystem by default.[citation needed] SDXC was announced at Consumer Electronics Show (CES) 2009 (January 7–10). At the same show, SanDisk and Sony also announced a comparable Memory Stick XC variant with the same 2 TB[17] maximum as SDXC,[18] and Panasonic announced plans to produce 64 GB SDXC cards.[19] On March 6, Pretec introduced the first SDXC card,[20] a 32 GB card with a read/write speed of 400 Mbit/s. But only early in 2010 did compatible host devices come onto the market, including Sony's Handycam HDR-CX55V camcorder, Canon's EOS 550D (also known as Rebel T2i) Digital SLR camera,[21] a USB card reader from Panasonic, and an integrated SDXC card reader from JMicron.[22] The earliest laptops to integrate SDXC card readers relied on a USB 2.0 bus, which does not have the bandwidth to support SDXC at full speed.[23]


In early 2010, commercial SDXC cards appeared from Toshiba (64 GB),[24][25] Panasonic (64 GB and 48 GB),[26] and SanDisk (64 GB).[27] 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 August 2017, SanDisk launched a 400 GB microSDXC card.[43] In January 2018, Integral Memory unveiled 512 GB microSDXC card.[44] In May 2018, PNY launched a 512 GB microSDXC card. In June 2018 Kingston announced the Canvas series for MicroSD cards which both are capable of capacities up to 512 GB,[45] in three variations, Select, Go!, and React.[46] In February 2019, Micron and SanDisk unveiled their microSDXC cards of 1 TB capacity.[47]

2018–present: SDUC[edit]

The Secure Digital Ultra Capacity (SDUC) format supports cards up to 128 TB[48] and offers speeds up to 985 MB/s.


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.[49][50][51] 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.

SD (SDSC)[edit]

Secure Digital Standard Capacity (SD) logo; the specification defines cards with a capacity of up to 2 GB

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:

  • Asymmetrical shape of the sides of the SD card prevent inserting it upside down (whereas an MMC goes in most of the way but makes no contact if inverted).
  • Most SD cards are 2.1 mm (0.083 inches) thick, compared to 1.4 mm (0.055 inches) for MMCs. The SD specification defines a card called Thin SD with a thickness of 1.4 mm, but they occur only rarely, 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. For a comparison table, see below.
  • While MMC uses a single pin for data transfers, the SD card added a four-wire bus mode for higher data rates.
  • The SD card added Content Protection for Recordable Media (CPRM) security circuitry for digital rights management (DRM) content-protection.
  • Addition of a write-protect notch

Full-size SD cards do not fit into the slimmer MMC slots, and other issues also affect the ability to use one format in a host device designed for the other.


Secure Digital High Capacity (SDHC) logo; the specification defines cards with a capacity of more than 2 GBup to 32 GB

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.[52][49] The SDHC trademark is licensed to ensure compatibility.[53]

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.

Version 2.0 also introduces a High-speed bus mode for both SDSC and SDHC cards, which doubles the original Standard Speed clock to produce 25 MB/s.[54]

SDHC host devices are required to accept older SD cards.[55] However, older host devices do not recognize SDHC or SDXC memory cards, although some devices can do so through a firmware upgrade.[56][better source needed] Older Windows operating systems released before Windows 7 require patches or service packs to support access to SDHC cards.[57][58][59]


Secure Digital eXtended Capacity logo; the specification defines cards with a capacity of more than 32 GBup to 2 TB

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,[60] compared to a limit of 32 GB[61] for SDHC cards in the SD 2.0 specification. SDXC adopts Microsoft's exFAT file system as a mandatory feature.[62]

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.[63] (this number has since been exceeded with SanDisk proprietary technology for 170 MB/s read, which isn’t 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)[64][65][66][67]

Version 4.0, introduced in June 2011, allows speeds of 156 MB/s to 312 MB/s over the four-lane (two differential lanes) UHS-II bus, which requires an additional row of physical pins.[63]

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.[68][69] The new ratings define a minimal write speed of 90 MB/s.[70][71]


Secure Digital Ultra Capacity (SDUC) logo; the specification defines cards with a capacity of more than 2 TBup to 128 TB

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[72] 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.[73] The SD Express interface can also be used with SDHC and SDXC cards.

exFAT filesystem[edit]

Main article: exFAT

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. However, SD cards can be reformatted to any file system required.

Windows Vista (SP1) and later[74] and OS X (10.6.5 and later) have native support for exFAT.[75][76] (Windows XP and Server 2003 can support exFAT via an optional update from Microsoft.)[77] 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.[78] 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.[79] However, SDXC cards can be reformatted to use any file system (such as ext4, UFS, or VFAT), alleviating the restrictions associated with exFAT availability.

Except for the change of file system, SDXC cards are mostly backward compatible with SDHC readers, and many SDHC host devices can use SDXC cards if they are first reformatted to the FAT32 file system.[80][81][82]

Nevertheless, in order to be fully compliant with the SDXC card specification, some SDXC-capable host devices are firmware-programmed to expect exFAT[clarification needed] on cards larger than 32 GB.[citation needed][dubious – discuss] Consequently, they may not accept SDXC cards reformatted as FAT32, even if the device supports FAT32 on smaller cards (for SDHC compatibility). Therefore, even if a file system is supported in general, it is not always possible to use alternative file systems on SDXC cards at all depending on how strictly the SDXC card specification has been implemented in the host device. This bears a risk of accidental loss of data, as a host device may treat a card with an unrecognized file system as blank or damaged and reformat the card.

The SD Association provides a formatting utility for Windows and Mac OS X that checks and formats SD, SDHC, SDXC, and SDUC cards.[83]



SD card speed is customarily rated by its sequential read or write speed. The sequential performance aspect is the most relevant for storing and retrieving large files (relative to block sizes internal to the flash memory), such as images and multimedia. Small data (such as file names, sizes and timestamps) falls under the much lower speed limit of random access, which can be the limiting factor in some use cases.[85][86][87]

With early SD cards, a few card manufacturers specified the speed as a "times" ("×") rating, which compared the average speed of reading data to that of the original CD-ROM drive. This was superseded by the Speed Class Rating, which guarantees a minimum rate at which data can be written to the card.[88]

The newer families of SD card improve card speed by increasing the bus rate (the frequency of the clock signal that strobes information into and out of the card). Whatever the bus rate, the card can signal to the host that it is "busy" until a read or a write operation is complete. Compliance with a higher speed rating is a guarantee that the card limits its use of the "busy" indication.


Default Speed[edit]

SD Cards will read and write at speeds of 12.5 MB/s.

High Speed[edit]

High Speed Mode (25 MB/s) was introduced to support digital cameras with 1.10 spec version.[89]

Ultra High Speed (UHS)[edit]

The Ultra High Speed (UHS) bus is available on some SDHC and SDXC cards.[90][91][92] The following ultra-high speeds are specified:


Specified in SD version 3.01.[93] Supports a clock frequency of 100 MHz (a quadrupling of the original "Default Speed"), which in four-bit transfer mode could transfer 50 MB/s (SDR50). UHS-I cards declared as UHS104 (SDR104) also support a clock frequency of 208 MHz, which could transfer 104 MB/s. Double data rate operation at 50 MHz (DDR50) is also specified in Version 3.01, and is mandatory for microSDHC and microSDXC cards labeled as UHS-I. In this mode, four bits are transferred when the clock signal rises and another four bits when it falls, transferring an entire byte on each full clock cycle, hence a 50 MB/s operation could be transferred using a 50 MHz clock.

There is a proprietary UHS-I extension primarily by SanDisk that increases transfer speed further to 170 MB/s, called DDR208 (or DDR200). Unlike UHS-II, it does not use additional pins. It achieves this by using the 208 MHz frequency of the standard SDR104 mode, but using DDR transfers.[94][95] This extension has since then been used by Lexar for their 1066x series (160 MB/s), Kingston Canvas Go Plus (170 MB/s) and the MyMemory PRO SD card (180 MB/s).

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 MB/s (full-duplex) or 312 MB/s (half-duplex) using an additional row of pins[96] (a total of 17 pins for full-size and 16 pins for micro-size cards).[90] 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 2021, there were more than 50 DSLR and compact system cameras using UHS-II.[97]


Version 6.0, released in February 2017, added two new data rates to the standard. FD312 provides 312 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.[98]

Cards that comply with UHS show Roman numerals 'I', 'II' or 'III' next to the SD card logo,[90][88] 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.

The higher speed rates are achieved by using a two-lane low voltage (0.4 V pp) differential interface. Each lane is capable of transferring up to 156 MB/s. In full-duplex mode, one lane is used for Transmit while the other is used for Receive. In half-duplex mode both lanes are used for the same direction of data transfer allowing a double data rate at the same clock speed. In addition to enabling higher data rates, the UHS-II interface allows for lower interface power consumption, lower I/O voltage and lower electromagnetic interference (EMI).

SD Express[edit]

Front and back of an SD Express card

The SD Express bus was released in June 2018 with SD specification 7.0. It uses a single PCIe lane to provide full-duplex 985 MB/s transfer speed. Supporting cards must also implement the NVM Express storage access protocol. The Express bus can be implemented by SDHC, SDXC, and SDUC cards. For legacy application use, SD Express cards must also support High Speed bus and UHS-I bus. The Express bus re-uses the pin layout of UHS-II cards and reserves the space for additional two pins that may be introduced in the future.[99]

Hosts which implement version 7.0 of the spec allow SD Cards to do direct memory access, which increases the attack surface of the host dramatically in the face of malicious SD cards.[100]

Version 8.0 was announced on 19 May 2020, with support for two PCIe lanes with additional row of contacts and PCIe 4.0 transfer rates, for a maximum bandwidth of 3938 MB/s.[101]

microSD Express[edit]

In February 2019, the SD Association announced microSD Express.[102] The microSD Express cards offer PCI Express and NVMe interfaces, as the June 2018 SD Express release did, alongside the legacy microSD interface for continued backwards compatibility. The SDA also released visual marks to denote microSD Express memory cards to make matching the card and device easier for optimal device performance.[103]

Bus speed Comparison[edit]

  • *: this speed is achievable using DDR208 controller




UHS50 UHS104 FullHalf
UHS-I UHS50 50 50 50 50 50 50
UHS104 50 104 104 104 104 104
UHS-II Full50 104 156 156 156 104
Half50 104 156 312 312 104
UHS-III 50 104 156 312 624 104
Express 50 104 104 104 104 985

NOTE: If the card reader uses the DDR208 controller on the UHS 1 pins, the card reader will perform at 180MB/s on applicable UHS 1 cards


64GB SanDisk Ultra microSDXC card (with UHS-I and UHS Speed Class 1 markings)
32GB Lexar 1000x microSDHC card (with UHS-II and UHS Speed Class 3 markings)
The front and back of the Sony 64GB SF-M Tough Series UHS-II SDXC Memory Card.

The SD Association defines standard speed classes for SDHC/SDXC cards indicating minimum performance (minimum serial data writing speed). Both read and write speeds must exceed the specified value. The specification defines these classes in terms of performance curves that translate into the following minimum read-write performance levels on an empty card and suitability for different applications:[93][88][106][107]

The SD Association defines three types of Speed Class ratings: the original Speed Class, UHS Speed Class, and Video Speed Class.

(Original) Speed Class[edit]

Speed Class ratings 2, 4, and 6 assert that the card supports the respective number of megabytes per second as a minimum sustained write speed for a card in a fragmented state.

Class 10 asserts that the card supports 10 MB/s as a minimum non-fragmented sequential write speed and uses a High Speed bus mode.[93] The host device can read a card's speed class and warn the user if the card reports a speed class that falls below an application's minimum need.[93] By comparison, the older "×" rating measured maximum speed under ideal conditions, and was vague as to whether this was read speed or write speed.

The graphical symbol for the speed class has a number encircled with 'C' (C2, C4, C6, and C10).

UHS Speed Class[edit]

UHS-I and UHS-II cards can use UHS Speed Class rating with two possible grades: class 1 for minimum write performance of at least 10 MB/s ('U1' symbol featuring number 1 inside 'U') and class 3 for minimum write performance of 30 MB/s ('U3' symbol featuring 3 inside 'U'), targeted at recording 4K video.[108] Before November 2013, the rating was branded UHS Speed Grade and contained grades 0 (no symbol) and 1 ('U1' symbol). Manufacturers can also display standard speed class symbols (C2, C4, C6, and C10) alongside, or in place of UHS speed class.

UHS memory cards work best with UHS host devices. The combination lets the user record HD resolution videos with tapeless camcorders while performing other functions. It is also suitable for real-time broadcasts and capturing large HD videos.

Video Speed Class[edit]

Video Speed Class defines a set of requirements for UHS cards to match the modern MLC NAND flash memory[70] and supports progressive 4K and 8K video with minimum sequential writing speeds of 6-90 MB/s.[68][88][106] The graphical symbols use 'V' followed by a number designating write speed (V6, V10, V30, V60, and V90).


  1. ^The necessary recording and playback speed class requirements may vary by device.

Application Performance Class[edit]

Application Performance Class is a newly defined standard from the SD Specification 5.1 and 6.0 which not only define sequential Writing Speeds but also mandates a minimum IOPS for reading and writing. Class A1 requires a minimum of 1500 reading and 500 writing operations per second, while class A2 requires 4000 and 2000 IOPS.[110] A2 class cards require host driver support as they use command queuing and write caching to achieve their higher speeds. If used in an unsupported host, they might even be slower than other A1 cards, and if power is lost before cached data is actually written from the card's internal RAM to the card's internal flash RAM, that data is likely to be lost.[111]

Name Minimum random IOPSMinimum sustained sequential writing
Read Write
SD App Performance 1.svg Application Performance Class 1 (A1)1500 IOPS500 IOPS10 MB/s
SD App Performance 2.svg Application Performance Class 2 (A2)4000 IOPS2000 IOPS

"×" rating[edit]

Main article: CD and DVD writing speed

The "×" rating, that was used by some card manufacturers and made obsolete by speed classes, is a multiple of the standard CD-ROM drive speed of 150 KB/s[113] (approximately 1.23 Mbit/s). Basic cards transfer data at up to six times (6×) the CD-ROM speed; that is, 900 KB/s or 7.37 Mbit/s. The 2.0 specification[clarification needed] defines speeds up to 200×, but is not as specific as Speed Classes are on how to measure speed. Manufacturers may report best-case speeds and may report the card's fastest read speed, which is typically faster than the write speed. Some vendors, including Transcend and Kingston, report their cards' write speed.[114] When a card lists both a speed class and an "×" rating, the latter may be assumed a read speed only.[citation needed]

Real-world performance[edit]

In applications that require sustained write throughput, such as video recording, the device might not perform satisfactorily if the SD card's class rating falls below a particular speed. For example, a high-definition camcorder may require a card of not less than Class 6, suffering dropouts or corrupted video if a slower card is used. Digital cameras with slow cards may take a noticeable time after taking a photograph before being ready for the next, while the camera writes the first picture.

The speed class rating does not totally characterize card performance. Different cards of the same class may vary considerably while meeting class specifications. A card's speed depends on many factors, including:

  • The frequency of soft errors that the card's controller must re-try
  • Write amplification: The flash controller may need to overwrite more data than requested. This has to do with performing read-modify-write operations on write blocks, freeing up (the much larger) erase blocks, while moving data around to achieve wear leveling.
  • File fragmentation: where there is not sufficient space for a file to be recorded in a contiguous region, it is split into non-contiguous fragments. This does not cause rotational or head-movement delays as with electromechanical hard drives, but may decrease speed⁠ ⁠ ⁠―  for instance, by requiring additional reads and computation to determine where on the card the file's next fragment is stored.

In addition, speed may vary markedly between writing a large amount of data to a single file (sequential access, as when a digital camera records large photographs or videos) and writing a large number of small files (a random-access use common in smartphones). A study in 2012 found that, in this random-access use, some Class 2 cards achieved a write speed of 1.38 MB/s, while all cards tested of Class 6 or greater (and some of lower Classes; lower Class does not necessarily mean better small-file performance), including those from major manufacturers, were over 100 times slower.[85] In 2014, a blogger measured a 300-fold performance difference on small writes; this time, the best card in this category was a class 4 card.[86]


Card security[edit]

Cards can protect their contents from erasure or modification, prevent access by non-authorized users, and protect copyrighted content using digital rights management.[citation needed]

Commands to disable writes[edit]

The host device can command the SD card to become read-only (to reject subsequent commands to write information to it). There are both reversible and irreversible host commands that achieve this.

Write-protect notch[edit]

Unlocked and locked SD cards
Sony 64GB SF-M Tough Series UHS-II SDXC Memory Card is one of the few cards in the market without a sliding tab on the write protect notch.

Most full-size SD cards have a "mechanical write protect switch" allowing the user to advise the host computer that the user wants the device to be treated as read-only. This does not protect the data on the card if the host is compromised: "It is the responsibility of the host to protect the card. The position of the write protect switch is unknown to the internal circuitry of the card."[115] Some host devices do not support write protection, which is an optional feature of the SD specification, and drivers and devices that do obey a read-only indication may give the user a way to override it.

The switch is a sliding tab that covers a notch in the card. The miniSD and microSD formats do not directly support a write protection notch, but they can be inserted into full-size adapters which do.

When looking at the SD card from the top, the right side (the side with the beveled corner) must be notched.

On the left side, there may be a write-protection notch. If the notch is omitted, the card can be read and written. If the card is notched, it is read-only. If the card has a notch and a sliding tab which covers the notch, the user can slide the tab upward (toward the contacts) to declare the card read/write, or downward to declare it read-only. The diagram to the right shows an orange sliding write-protect tab in both the unlocked and locked positions.

Cards sold with content that must not be altered are permanently marked read-only by having a notch and no sliding tab.

Card password[edit]

MicroSD to SD adapter (left), microSD to miniSD adapter (middle), microSD card (right)

A host device can lock an SD card using a password of up to 16 bytes, typically supplied by the user. A locked card interacts normally with the host device except that it rejects commands to read and write data. A locked card can be unlocked only by providing the same password. The host device can, after supplying the old password, specify a new password or disable locking. Without the password (typically, in the case that the user forgets the password), the host device can command the card to erase all the data on the card for future re-use (except card data under DRM), but there is no way to gain access to the existing data.

Windows Phone 7 devices use SD cards designed for access only by the phone manufacturer or mobile provider. An SD card inserted into the phone underneath the battery compartment becomes locked "to the phone with an automatically generated key" so that "the SD card cannot be read by another phone, device, or PC".[116]Symbian devices, however, are some of the few that can perform the necessary low-level format operations on locked SD cards. It is therefore possible to use a device such as the Nokia N8 to reformat the card for subsequent use in other devices.[117]

smartSD cards[edit]

A smartSD memory card is a microSD card with an internal "secure element" that allows the transfer of ISO 7816 Application Protocol Data Unit commands to, for example, JavaCard applets running on the internal secure element through the SD bus.[118]

Some of the earliest versions of microSD memory cards with secure elements were developed in 2009 by DeviceFidelity, Inc.,[119][120] a pioneer in near field communication (NFC) and mobile payments, with the introduction of In2Pay and CredenSE products, later commercialized and certified for mobile contactless transactions by Visa in 2010.[121] DeviceFidelity also adapted the In2Pay microSD to work with the Apple iPhone using the iCaisse, and pioneered the first NFC transactions and mobile payments on an Apple device in 2010.[122][123][124]

Various implementations of smartSD cards have been done for payment applications and secured authentication.[125][126] In 2012 Good Technology partnered with DeviceFidelity to use microSD cards with secure elements for mobile identity and access control.[127]

microSD cards with Secure Elements and NFC (near field communication) support are used for mobile payments, and have been used in direct-to-consumer mobile wallets and mobile banking solutions, some of which were launched by major banks around the world, including Bank of America, US Bank, and Wells Fargo,[128][129][130] while others were part of innovative new direct-to-consumer neobank programs such as moneto, first launched in 2012.[131][132][133][134]

microSD cards with Secure Elements have also been used for secure voice encryption on mobile devices, which allows for one of the highest levels of security in person-to-person voice communications.[135] Such solutions are heavily used in intelligence and security.

In 2011, HID Global partnered with Arizona State University to launch campus access solutions for students using microSD with Secure Element and MiFare technology provided by DeviceFidelity, Inc..[136][137] This was the first time regular mobile phones could be used to open doors without need for electronic access keys.

Vendor enhancements[edit]

SD cards with dual interfaces: SD and USB

Vendors have sought to differentiate their products in the market through various vendor-specific features:

  • Integrated Wi-Fi – Several companies produce SD cards with built-in Wi-Fi transceivers supporting static security (WEP 40; 104; and 128, WPA-PSK, and WPA2-PSK). The card lets any digital camera with an SD slot transmit captured images over a wireless network, or store the images on the card's memory until it is in range of a wireless network. Examples include: Eye-Fi / SanDisk, Transcend Wi-Fi, Toshiba FlashAir, Trek Flucard, PQI Air Card and LZeal ez Share.[138] Some models geotag their pictures.
  • Pre-loaded content – In 2006, SanDisk announced Gruvi, a microSD card with extra digital rights management features, which they intended as a medium for publishing content. SanDisk again announced pre-loaded cards in 2008, under the slotMusic name, this time not using any of the DRM capabilities of the SD card.[139] In 2011, SanDisk offered various collections of 1000 songs on a single slotMusic card for about $40,[140] now restricted to compatible devices and without the ability to copy the files.
  • Integrated USB connector – The SanDiskSD Plus product can be plugged directly into a USB port without needing a USB card reader.[141] Other companies introduced comparable products, such as the Duo SD product of OCZ Technology and the 3 Way (microSDHC, SDHC, and USB) product of A-DATA, which was available in 2008 only.
  • Different colors – SanDisk has used various colors of plastic or adhesive label, including a "gaming" line in translucent plastic colors that indicated the card's capacity.
  • Integrated display – In 2006, A-DATA announced a Super Info SD card with a digital display that provided a two-character label and showed the amount of unused memory on the card.[142]

SDIO cards[edit]

Camera using the SDIO interface to connect to some HP iPAQ devices

A SDIO (Secure Digital Input Output) card is an extension of the SD specification to cover I/O functions. SDIO cards are only fully functional in host devices designed to support their input-output functions (typically PDAs like the Palm Treo, but occasionally laptops or mobile phones). These devices can use the SD slot to support GPS receivers, modems, barcode readers, FM radio tuners, TV tuners, RFID readers, digital cameras, and interfaces to Wi-Fi, Bluetooth, Ethernet, and IrDA. Many other SDIO devices have been proposed, but it is now more common for I/O devices to connect using the USB interface.

SDIO cards support most of the memory commands of SD cards. SDIO cards can be structured as eight logical cards, although currently, the typical way that an SDIO card uses this capability is to structure itself as one I/O card and one memory card.

The SDIO and SD interfaces are mechanically and electrically identical. Host devices built for SDIO cards generally accept SD memory cards without I/O functions. However, the reverse is not true, because host devices need suitable drivers and applications to support the card's I/O functions. For example, an HP SDIO camera usually does not work with PDAs that do not list it as an accessory. Inserting an SDIO card into any SD slot causes no physical damage nor disruption to the host device, but users may be frustrated that the SDIO card does not function fully when inserted into a seemingly compatible slot. (USB and Bluetooth devices exhibit comparable compatibility issues, although to a lesser extent thanks to standardized USB device classes and Bluetooth profiles.)

The SDIO family comprises Low-Speed and Full-Speed cards. Both types of SDIO cards support SPI and one-bit SD bus types. Low-Speed SDIO cards are allowed to also support the four-bit SD bus; Full-Speed SDIO cards are required to support the four-bit SD bus. To use an SDIO card as a "combo card" (for both memory and I/O), the host device must first select four-bit SD bus operation. Two other unique features of Low-Speed SDIO are a maximum clock rate of 400 kHz for all communications, and the use of Pin 8 as "interrupt" to try to initiate dialogue with the host device.[143]

Ganging cards together

The one-bit SD protocol was derived from the MMC protocol, which envisioned the ability to put up to three cards on a bus of common signal lines. The cards use open collector interfaces, where a card may pull a line to the low voltage level; the line is at the high voltage level (because of a pull-up resistor) if no card pulls it low. Though the cards shared clock and signal lines, each card had its own chip select line to sense that the host device had selected it.[citation needed]

The SD protocol envisioned the ability to gang 30 cards together without separate chip select lines. The host device would broadcast commands to all cards and identify the card to respond to the command using its unique serial number.[citation needed]

In practice, cards are rarely ganged together because open-collector operation has problems at high speeds and increases power consumption. Newer versions of the SD specification recommend separate lines to each card.[citation needed]


Host devices that comply with newer versions of the specification provide backward compatibility and accept older SD cards.[55] For example, SDXC host devices accept all previous families of SD memory cards, and SDHC host devices also accept standard SD cards.

Older host devices generally do not support newer card formats, and even when they might support the bus interface used by the card,[50] there are several factors that arise:

  • A newer card may offer greater capacity than the host device can handle (over 4 GB for SDHC, over 32 GB for SDXC).
  • A newer card may use a file system the host device cannot navigate (FAT32 for SDHC, exFAT for SDXC)
  • Use of an SDIO card requires the host device be designed for the input/output functions the card provides.
  • The hardware interface of the card was changed starting with the version 2.0 (new high-speed bus clocks, redefinition of storage capacity bits) and SDHC family (Ultra-high speed (UHS) bus)
  • UHS-II has physically more pins but is backwards compatible to UHS-I and non-UHS for both slot and card.[90]
  • Some vendors produced SDSC cards above 1 GB before the SDA had standardized a method of doing so.


Due to their compact size, Secure Digital cards are used in many consumer electronic devices, and have become a widespread means of storing several gigabytes of data in a small size. Devices in which the user may remove and replace cards often, such as digital cameras, camcorders, and video game consoles, tend to use full-sized cards. Devices in which small size is paramount, such as mobile phones, action cameras such as the GoPro Hero series, and camera drones, tend to use microSD cards.[144][145]

Mobile phones[edit]

The microSD card has helped propel the smartphone market by giving both manufacturers and consumers greater flexibility and freedom.

While cloud storage depends on stable internet connection and sufficiently voluminous data plans, memory cards in mobile devices provide location-independent and private storage expansion with much higher transfer rates and no latency (engineering)(§ Real-world performance), enabling applications such as photography and video recording. While data stored internally on bricked devices is inaccessible, data stored on the memory card can be salvaged and accessed externally by the user as mass storage device. A benefit over USB on the go storage expansion is uncompromised ergonomy. The usage of a memory card also protects the mobile phone's non-replaceable internal storage from weardown from heavy applications such as excessive camera usage and portable FTP server hosting over WiFi Direct. Due to the technical development of memory cards, users of existing mobile devices are able to expand their storage further and priceworthier with time.[146][147][148]

Recent versions of major operating systems such as Windows Mobile and Android allow applications to run from microSD cards, creating possibilities for new usage models for SD cards in mobile computing markets, as well as clearing available internal storage space.[149]

SD cards are not the most economical solution in devices that need only a small amount of non-volatile memory, such as station presets in small radios. They may also not present the best choice for applications that require higher storage capacities or speeds as provided by other flash card standards such as CompactFlash. These limitations may be addressed by evolving memory technologies, such as the new SD 7.0 specifications which allow storage capabilities of up to 128 TB[150].[151]

Many personal computers of all types, including tablets and mobile phones, use SD cards, either through built-in slots or through an active electronic adapter. Adapters exist for the PC card, ExpressBus, USB, FireWire, and the parallel printer port. Active adapters also let SD cards be used in devices designed for other formats, such as CompactFlash. The FlashPath adapter lets SD cards be used in a floppy disk drive.

Some devices such as the Samsung Galaxy Fit (2011) and Samsung Galaxy Note 8.0 (2013) have an SD card compartment located externally and accessible by hand, while it is located under the battery cover on other devices. More recent mobile phones use a pin-hole ejection system for the tray which houses both the memory card and SIM card.


SamsungPro 64 GB microSDXC original (left) and counterfeit (right): The counterfeit claims to have 64 GB in capacity, but only 8 GB (Class 4 speed) are usable: When trying to write more than 8 GB, data lossoccurs. Also used for SanDisk64 GB fakes.
Images of genuine, questionable, and fake/counterfeit microSD (Secure Digital) cards before and after decapsulation. Details at source, photo by Andrew Huang.

Commonly found on the market are mislabeled or counterfeit Secure Digital cards that report a fake capacity or run slower than labeled.[152][153][154] Software tools exist to check and detect counterfeit products.[155][156] Detection of counterfeit cards usually involves copying files with random data to the SD card until the card's capacity is reached, and copying them back. The files that were copied back can be tested either by comparing checksums (e.g. MD5), or trying to compress them. The latter approach leverages the fact that counterfeited cards let the user read back files, which then consist of easily compressible uniform data (for example, repeating 0xFFs).

Digital cameras[edit]

SD/MMC cards replaced Toshiba's SmartMedia as the dominant memory card format used in digital cameras. In 2001, SmartMedia had achieved nearly 50% use, but by 2005 SD/MMC had achieved over 40% of the digital camera market and SmartMedia's share had plummeted by 2007.

At this time, all the leading digital camera manufacturers used SD in their consumer product lines, including Canon, Casio, Fujifilm, Kodak, Leica, Nikon, Olympus, Panasonic, Pentax, Ricoh, Samsung, and Sony. Formerly, Olympus and Fujifilm used XD-Picture Cards (xD cards) exclusively, while Sony only used Memory Stick; by early 2010 all three supported SD.

Some prosumer and professional digital cameras continued to offer CompactFlash (CF), either on a second card slot or as the only storage, as CF supports much higher maximum capacities and historically was cheaper for the same capacity.

Secure Digital memory cards can be used in Sony XDCAM EX camcorders with an adapter[157] and in Panasonic P2 card equipment with a MicroP2 adapter.

Personal computers[edit]

Although many personal computers accommodate SD cards as an auxiliary storage device using a built-in slot, or can accommodate SD cards by means of a USB adapter, SD cards cannot be used as the primary hard disk through the onboard ATA controller, because none of the SD card variants support ATA signalling. Primary hard disk use requires a separate SD controller chip[158] or an SD-to-CompactFlash converter. However, on computers that support bootstrapping from a USB interface, an SD card in a USB adapter can be the primary hard disk, provided it contains an operating system that supports USB access once the bootstrap is complete.

In laptop and tablet computers, memory cards in an integrated card reader offer an ergonomical benefit over USB flash drives, as the latter sticks out of the device, and the user would need to be cautious not to bump it while transporting the device, which could damage the USB port. Memory cards have a unified shape and do not reserve a USB port when inserted into a computer's dedicated card slot.

Since late 2009, newer Apple computers with installed SD card readers have been able to boot in macOS from SD storage devices, when properly formatted to Mac OS Extended file format and the default partition table set to GUID Partition Table.[159] (See Other file systems below).

SD cards are increasing in usage and popularity among owners of vintage computers like 8-bit Atari. For example SIO2SD (SIO is an Atari port for connecting external devices) is used nowadays. Software for an 8-bit Atari may be included on one SD card that may have less than 4-8 GB of disk size (2019).[160]

Embedded systems[edit]

In 2008, the SDA specified Embedded SD, "leverag[ing] well-known SD standards" to enable non-removable SD-style devices on printed circuit boards.[161] However this standard was not adopted by the market while the MMC standard became the de facto standard for embedded systems. SanDisk provides such embedded memory components under the iNAND brand.[162]

Most modern microcontrollers have built-in SPI logic that can interface to an SD card operating in its SPI mode, providing non-volatile storage. Even if a microcontroller lacks the SPI feature, the feature can be emulated by bit banging. For example, a home-brew hack combines spare General Purpose Input/Output (GPIO) pins of the processor of the LinksysWRT54G router with MMC support code from the Linux kernel.[163] This technique can achieve throughput of up to 1.6 Mbit/s.

Music distribution[edit]

Prerecorded microSDs have been used to commercialize music under the brands slotMusic and slotRadio by SanDisk and MQS by Astell&Kern.

Technical details[edit]

Physical size[edit]

The SD card specification defines three physical sizes. The SD and SDHC families are available in all three sizes, but the SDXC and SDUC families are not available in the mini size, and the SDIO family is not available in the micro size. Smaller cards are usable in larger slots through use of a passive adapter.


Size comparison of families: SD (blue), miniSD (green), microSD (red)
  • 32 mm × 24 mm × 2.1 mm (1+17⁄64 in × 15⁄16 in × 5⁄64 in)
  • 32 mm × 24 mm × 1.4 mm (1+17⁄64 in × 15⁄16 in × 1⁄16 in) (as thin as MMC) for Thin SD (rare)


  • miniSD, miniSDHC, miniSDIO
  • 21.5 mm × 20 mm × 1.4 mm (27⁄32 in × 25⁄32 in × 1⁄16 in)


The micro form factor is the smallest SD card format.[164]

  • microSD, microSDHC, microSDXC, microSDUC
  • 15 mm × 11 mm × 1 mm (19⁄32 in × 7⁄16 in × 3⁄64 in)

Transfer modes[edit]

Cards may support various combinations of the following bus types and transfer modes. The SPI bus mode and one-bit SD bus mode are mandatory for all SD families, as explained in the next section. Once the host device and the SD card negotiate a bus interface mode, the usage of the numbered pins is the same for all card sizes.

  • SPI bus mode:Serial Peripheral Interface Bus is primarily used by embedded microcontrollers. This bus type supports only a 3.3-volt interface. This is the only bus type that does not require a host license.[citation needed]
  • One-bit SD bus mode: Separate command and data channels and a proprietary transfer format.
  • Four-bit SD bus mode: Uses extra pins plus some reassigned pins. This is the same protocol as the one-bit SD bus mode which uses one command and four data lines for faster data transfer. All SD cards support this mode. UHS-I and UHS-II require this bus type.
  • Two differential lines SD UHS-II mode: Uses two low-voltage differential interfaces to transfer commands and data. UHS-II cards include this interface in addition to the SD bus modes.

The physical interface comprises 9 pins, except that the miniSD card adds two unconnected pins in the center and the microSD card omits one of the two VSS (Ground) pins.[165]

Official pin numbers for each card type (top to bottom): MMC, SD, miniSD, microSD. This shows the evolution from the older MMC, on which SD is based. NOTE: This drawing doesn't show 8 new UHS-II contacts that were added in spec 4.0.
1112nCSIPPSPI Card Select [CS] (Negative logic)
2223DIIPPSPI Serial Data In [MOSI]
333 VSSSSGround
5555CLKIPPSPI Serial Clock [SCLK]
7777DOOPPSPI Serial Data Out [MISO]
Unused (memory cards)
Interrupt (SDIO cards) (negative logic)
10 NC..Reserved
11 NC..Reserved
1112CDI/O.Card detection (by host), and
non-SPI mode detection (by card)
333 VSSSSGround
5555CLKIPPSerial clock
7777DAT0I/OPPSD Serial Data 0
Unused (memory cards)
Interrupt (SDIO cards) (negative Logic)
10 NC..Reserved
11 NC..Reserved
.112DAT3I/OPPSD Serial Data 3
.33 VSSSSGround
.555CLKIPPSerial clock
.777DAT0I/OPPSD Serial Data 0
SD Serial Data 1 (memory cards)
Interrupt Period (SDIO cards share pin via protocol)
991DAT2I/OPPSD Serial Data 2
10 NC..Reserved
11 NC..Reserved


  1. Direction is relative to card. I = Input, O = Output.
  2. PP = Push-Pull logic, OD = Open-Drain logic.
  3. S = Power Supply, NC = Not Connected (or logical high).


Inside a 2 GB SD card: two NAND flashchips (top and middle), SD controller chip (bottom)
Inside a 16 GB SDHC card

Command interface[edit]

SD cards and host devices initially communicate through a synchronous one-bit interface, where the host device provides a clock signal that strobes single bits in and out of the SD card. The host device thereby sends 48-bit commands and receives responses. The card can signal that a response will be delayed, but the host device can abort the dialogue.[93]

Through issuing various commands, the host device can:[93]

  • Determine the type, memory capacity, and capabilities of the SD card
  • Command the card to use a different voltage, different clock speed, or advanced electrical interface
  • Prepare the card to receive a block to write to the flash memory, or read and reply with the contents of a specified block.

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.

Electrical interface[edit]

All SD card families initially use a 3.3 volt electrical interface. On command, SDHC and SDXC cards can switch to 1.8 V operation.[93]

At initial power-up or card insertion, the host device selects either the Serial Peripheral Interface (SPI) bus or the one-bit SD bus by the voltage level present on Pin 1. Thereafter, the host device may issue a command to switch to the four-bit SD bus interface, if the SD card supports it. For various card types, support for the four-bit SD bus is either optional or mandatory.[93]

After determining that the SD card supports it, the host device can also command the SD card to switch to a higher transfer speed. Until determining the card's capabilities, the host device should not use a clock speed faster than 400 kHz. SD cards other than SDIO (see below) have a "Default Speed" clock rate of 25 MHz. The host device is not required to use the maximum clock speed that the card supports. It may operate at less than the maximum clock speed to conserve power.[93] Between commands, the host device can stop the clock entirely.

Achieving higher card speeds[edit]


2014 card fastest sd

SanDisk Extreme Pro UHS-II Memory Card Review – Fastest SD Card on The Planet!

When it comes to SD card performance, we typically expect to see speeds typical of the industry standard of 90 MB/s. You can imagine the look on our faces when we receive a SD card that advertises read speeds of up to 280 MB/s. Ok, so maybe our jaws were touching the floor. That is exactly what happened when the SanDisk Extreme PRO UHS-II Card showed up at our front door.


Our report today will examine and test the SanDisk Extreme PRO SDHC card as it makes fluid use of the newest UHS-II standard, as well as the SanDisk Extreme PRO SD card reader. Let’s take a closer look and see how SanDisk has created the fastest SD card family in the world.


First, there are a few acronyms and short forms that follow the name of the SD card. Some of you may not know what they mean, some of you may. So, let’s run through it quickly to keep everyone on the same page.


SD, SDHC and SDXC speak to the cards available capacity first and foremost. When considering the size necessary for your photography or videography, your storage device will be your ultimate determinant. Obviously a flash card with a lower capacity will hold less videos and photos, which is pretty straight forward. If you have an SD (Secure Digital) card, you are probably going to want to upgrade that shortly, as that is an older technology that accompanied the first digital photography and videography devices. With it, you will find not only lower capacities, but slower transfer speeds.

To go the next step up to a more prevalent storage option, especially for photography enthusiasts and weekend photo shoots, is SDHC (Secure Digital High Capacity). SDHC cards can allow for capacities of up to 32GB, and transfer speeds of up to 42 MB/s. If you are looking to shoot video in a higher resolution, then you will find yourself looking one step further with SDXC (Secure Digital Xtended Capacity). SDXC can allow for capacities greater than 32GB, and have a maximum write speed of up to 95 MB/s.


If you are interested more in videography, than the next acronym is your key point to look for, especially if you are worried about transfer speeds. If you have a flash card handy, take a look at it, you may notice that there is a number that has a circle around it. This is your class rating, which denotes the guaranteed minimum write speed. To give you an example if you have a ’4′ within your circle, your flash card is guaranteed to write at a minimum of 4 MB/s. When you start to get up to higher minimum write speeds, you will notice that the number will not increase past ’10′, instead the denotation changes to UHS-1, or a U with a ’1′ or a ’3′ within it. ‘Ultra High Speed 1′ would guarantee minimum write speeds of 10 MB/s and UHS-1 Speed Class 3 would denote minimum speeds of 30 MB/s. If your DSLR or video camera is not capable of UHS-1, than the flash card will revert back to Class 10 performance.

UHS-II is the newest ultra high-speed memory card standard and accounts for speeds just above 150MB/s through single lane access and over 300MB/s for dual lane.


Take a look at the back of the SD card … notice anything different? The typical set of SD Card contacts that are usually found on the top of the SD card’s back, have mutated. There is an additional set of contacts below the ‘typical’ set of contacts now accounting for this dual lane access; the new set of contacts work exclusively with those high-speed UHS-II signals.  The SanDisk Extreme PRO SD card is available in 16, 32 and 64 GB capacities, which is your typical set of available consumer capacities. A quick check of Amazon shows that the 16 GB version is available to be purchased for $73.95, the 32GB at $124.95 and the 64GB at $229.95.


The SanDisk SD card is listed to reach read speeds of up to 280 MB/s, and write speeds can reach up to 250 MB/s. Ok, I’ll let you catch your breath before we continue … These performance specifications are ridiculous! It’s completely unheard of that a SD card could reach such high scores. To think, were inching closer and closer to SSD performance potential in a unit that is roughly 1/16th the size of a SSD. Add to that the fact that the SanDisk Extreme Pro is shockproof, x-ray proof and waterproof and, unbelievably, comes with a lifetime limited warranty, and this card is crafting its own place in the world.


To reach these higher transfer speeds, you would need to use a specific USB 3.0 card reader (and motherboard capable of SuperSpeed) to get the full potential. With our test bench we utilized the SanDisk Extreme PRO UHS-II SD Reader/Writer. This is a simple plug-and-play device that you will connect into your USB 3.0 port on your system, and insert your flash card to transfer content. The SanDisk Extreme PRO card reader is specially designed for this memory card, as it can  reach those extra set of contacts that we have discussed previously.


Additionally, the Extreme PRO SD Card reader  is backwards compatible to USB 2.0. This means that if your USB port on your computer is not blue in colour, then you can still use the drive. You will just receive that annoying notification from Windows letting you know that the drive can perform faster in a USB 3.0 port.If your computer is not equipped with the latest USB technology, then we encourage you to have a look at our report of the HighPoint 4-Port HBA. This PCIe expansion card easily allows you to add four additional USB ports to your system, as well as the addition of USB 3.0 technology.


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16GBATTOcameracard readerCrystal DiskMarkExtreme promediaSandiskSDSDHCsecure digitalUHS-II2014-06-17

+Chris Jolliffe

SD Cards and the Readers Transfer Speed Differences

SanDisk Announces World's Fastest SD Card

SanDisk Corporation (NASDAQ: SNDK), a global leader in flash storage solutions, today announced the SanDisk Extreme PRO SDHC/SDXC UHS-II card. It is the world's fastest SD memory card, and is based on the latest high performance SD specification. The new SanDisk Extreme PRO SD UHS-II card offers up to 250 MB/s write speeds for continuous burst mode shooting and transfer speeds of up to 280 MB/s for maximum workflow efficiency. The SanDisk Extreme PRO SD UHS-II card is UHS Speed Class 3 (U3) enabled, a new specification allowing for high-quality 4K video recording.

"Camera manufacturers are rapidly introducing camera models for both consumers and professionals that are capable of higher burst rates and 4K video capture. Accordingly, memory card technology must move at a similar pace to provide users with the substantial performance required to take full advantage of these features," said Christopher Chute, research director, Worldwide Digital Imaging, IDC. "The higher levels of performance delivered by the new SanDisk Extreme PRO SD UHS-II card will help ensure that photographers, videographers and filmmakers are able to take advantage of the full capabilities of new professional-grade cameras."
Optimized for the next generation of high-end DSLRs and pro video cameras that support the UHS-II standard, the SanDisk Extreme PRO SD UHS-II card delivers the uncompromising results that professional photographers demand. Fast write speeds of up to 250MB/s allows users to take high-resolution images, such as RAW and JPEG, in succession. In addition to industry-leading read and write speeds, the card offers the highest video performance available for sustained video capture of 30MB/s (U3), allowing capture of cinema-quality 4K, 3D and Full HD videos.

"The new SanDisk Extreme PRO SD UHS-II card shatters the existing barrier of UHS-I limitations, delivering speeds up to three times faster than current cards," said Susan Park, director, product marketing, SanDisk. "As leaders in the flash storage industry, our goal is to deliver the fastest memory cards on the market, enabling next generation cameras to take advantage of new levels of performance. This is another example of our legacy of innovation and technology leadership in the digital imaging and video industries."

"FUJIFILM has announced the world's first UHS-II compatible digital camera, the X-T1," said Toshihisa Iida, senior manager, Optical Device and Electronic Imaging Products Division, FUJIFILM Corporation. "The performance delivered by the new SanDisk Extreme PRO SD UHS-II card will ensure that photographers can take full advantage of the FUJIFILM X-T1, which provides an advanced photographic experience including the highest-standard image quality, as well as fast shooting speed and response."

SanDisk Extreme PRO memory cards are tested for durability under extreme temperature conditions and backed by a lifetime limited warranty. The cards also include a one-year downloadable offer for RescuePRO Deluxe media recovery software5, which helps photographers recover their images in case of accidental deletion.

You will also be interested:

Nikon D5300 Memory Card Slot

Nikon D5300 SD Memory Cards

Published: August 22, 2014

The Nikon D5300 DSLR offers enthusiast photographers a well-optioned camera at a mid-level price. It shares many features with the Nikon D7100, including a relatively small buffer which can slow down continuous shooting. This means the D5300 will benefit from using a memory card with a fast write speed. In our tests, the D5300 was able achieve over 50MB/s write speed when using the fast SD cards.

D5300 SD Card Test — Write Speed

Test date: August 11, 2014

To begin fill each SD card with images to write what is essentially random data to the card and approximates actual use. We then format the card in the D5300. The camera is set to Continuous High, image format 14-bit compressed RAW (.NEF) image format and manual mode. We take a burst of 16 images of a static test scene. We measure the write speed by dividing the total bytes written by the elapsed time measured using the card access light. One megabyte is equal to 1,048,576 bytes. The test is then repeated 5 times and the average results appear below.

D5300 Continuous Shooting Test — SD Card Comparison

This test measures how many shots the D5300 can take in 30 seconds. The test is performed using three image settings: RAW+JPEG, RAW, and JPEG. In testing continuous shooting performance camera settings as well as the content of the image affect the number of shots. Our test uses a detailed test scene and camera settings to create relatively large file sizes to reveal the difference between memory cards.

RAW: 14-bit compressed (the highest RAW option on the D5300)
JPEG: Fine, Large, optimal quality

D5300 Continuous Shooting — Analysis

Here we see the D5300 is limited by its buffer. It was able to shoot the first 5 RAW+JPEG shots, 5 or 6 RAW, and at least 12 JPEG before the frame rate slowed down. This number is higher with faster cards. In JPEG mode, the fastest three cards were able to sustain full speed for the entire test. In RAW and RAW+JPEG the slower cards caused the frame rate to drop significantly after the buffer filled.

Recommended Nikon D5300 Memory Cards

The fastest card for the D5300 is the SanDisk Extreme Pro 32GB SDHC. It was the clear winner, averaging 53.7MB/s write speed. Close behind it are the Toshiba Exceria Type 1 and the Samsung PRO which both averaged above 51MB/s write speed. All of these cards allow the D5300 to operate at maximum potential. The Samsung has the best value, but it isn't a card officially approved by Nikon. We had no issues in our testing.

The second tier is comprised of the Toshiba Exceria Type 2, SanDisk Extreme Plus and Sony "94MB/s" (claimed read speed), all of which averaged around 40MB/s write speed. These cards offer about 80% of the speed of the fastest cards at a lower price point.

Choosing any of the slower cards will have an impact on shooting performance. There was a significant drop in the number of frames we could get in a given time, and the camera slowed noticeably after taking 6 RAW images. When trying to capture fast action you have to keep that in mind.


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