SD card logo
|capacity||SD: 8 MB to 2 GB SDHC: 4 GB to 32 GB SDXC: 32 GB to 2 TB SDUC: 2 TB to 128 TB
SD: 24mm × 32.0mm ×
2.1mm miniSD: 20mm × 21.5mm ×
1.4mm microSD: 11mm × 15.0mm × 1.0mm
|up to 300 MB / s|
|up to 260 MB / s|
|use||Mobile devices: digital cameras , cell phones , MP3 players , camcorders , single-board computers|
The SD card was developed in 2001 by SanDisk , Toshiba and Panasonic on the basis of the older MMC standard. The name Secure Digital is derived from additional hardware functions for digital rights management (DRM). By means of a key stored in the protected memory area, the card is intended to prevent unauthorized playback of protected media files. The encryption is based on the CPRM method of the 4C Entity Consortium, which is used in a similar way ( CPPM ) for DVD-Audio .
The industrial specification is under lock and key and can only be viewed by the paying licensees of the SD card association. According to its own information, this association has around 900 members worldwide (as of 2020) with 460 trademarks or company brands. Regardless of this, however, some of the access logs are disclosed without access to the protected memory area. An international standard by committees of the IEC or ISO does not exist.
On the hardware side, access is via a separate protocol called "SD Bus". Alternatively, the SPI can be used, although SD cards do not support newer functions and guaranteed speeds . The SD bus can use various access methods such as 1- or 4-bit serial data transmission. If the initialization sequence specified in the specification is not followed exactly, the host controller of the card reader / PDA is switched off.
Structure of the map
The memory card has an integrated controller , is 24 mm × 32 mm × 2.1 mm in size and originally had a capacity of 8 megabytes . Subsequent models doubled the storage space (16, 32, ... MB) so that capacities of up to 1 terabyte are available. However, there are also exceptions to this scheme.
There is a small slider for write protection on the side of an SD card. The position of this slide can be recorded by a switch contact in the card holder and evaluated using the device software. If the slide is in the direction of the card contacts, this signals the release for write access. The position of the slide is not recognized by the card itself, so the card itself cannot refuse write access if the user expresses this request using the slide, but it is always up to the read / write device to implement this user request.
The miniSD was developed for small devices . At 20 mm × 21.5 mm × 1.4 mm, it is about half the size of the SD card. With the help of an adapter that is often supplied with the purchase, it fits into normal SD slots. These small cards are offered with a storage capacity of up to 16 GB (miniSDHC). Since production has ceased in September 2009, the card has disappeared from sale. Devices that require miniSD can use microSD memory cards via an adapter instead.
The microSD card (formerly known as TransFlash ) is even smaller than the miniSD. At 11 mm × 15 mm × 1.0 mm , it is just the size of a fingernail and in 2011 it was the smallest Flash ROM memory card in the world. The first microSD card produced for the mass market with a storage capacity of 1 TB appeared in April 2019 and was available for around € 500. The manufacturer stated the read rate to be 160 MB / s and the write rate to be 90 MB / s.
Both miniSD and microSD (since 2005) can be converted to SD card format using an adapter. A microSD card can also be converted to miniSD format using an adapter.
For communication with the card reader, SD cards have 9 pins, miniSD cards 11 pins and microSD cards 8 pins on the bottom.
|1||2||CD / DAT3||I / O / PP||Card recognition / data line [bit 3]|
|2||3||CMD||PP||Command and response|
|3||-||GND1 / VSS1||S.||Dimensions|
|4th||VDD||S.||Power supply (DC 2.7 ... 3.6 V)|
|6th||GND2 / VSS2||S.||Dimensions|
|7th||DAT0||I / O / PP||Data line [bit 0]|
|8th||DAT1||I / O / PP||Data line [bit 1]|
|9||1||DAT2||I / O / PP||Data line [bit 2]|
Since 2005 there have also been SD cards that have a USB port and can be connected to a USB type A socket without an adapter or memory card reader . The USB port is usually protected by a cover that can be folded away or pulled off.
WiFi and GPS
SD cards with internal WLAN function have been available since mid-2008 , among others marketed as Wi-Fi SD card from Transcend , FlashAir from Toshiba and Eye-Fi Card . Depending on the card type, PC synchronization , Internet upload via hotspots or wireless access points are possible, as is the storage of the geographic data of the recording location. Thanks to the dimensions of SD cards, they fit into common camera models. As far as geographic coordinates are used, they come from a database of local WLAN stations ( Skyhook ) and are added to the Exif data when the images are passed on to the Internet . These cards will not work with every device.
SD card (SD 1.0 and SD 1.1)
The consortium for SD cards defines a card capacity of up to 1 GB (SD 1.0) and 2 GB (SD 1.1) with the file system FAT (FAT 12/16).
- In various devices, the larger card is simply displayed and partitioned with a capacity of 1 GB.
- Larger cards that are not designed according to the SD 1.0 or SD 1.1 industry standard are not compatible in older devices, and they also do not work in some SDHC devices.
- Devices that only support SD 1.0 industry standard (especially older card readers) sometimes read 2 GB cards, but cause errors in the memory area above 1 GB.
- Cards with a capacity of 4 GB that are sold as SD cards, i.e. not SDHC cards, do not meet the specifications.
SDHC cards do not work in devices that can only work with SD cards. Since this is not always noted on the device, you should test the interaction between card and reader before buying. The dimensions correspond to those of SD cards. SDHC-compatible hardware, on the other hand, is backwards compatible with SD cards. SDHC card readers are usually fully upwardly compatible with the SDXC standard, provided the computer's operating system supports exFAT . The computer operating systems from the time before SDXC are exFAT-capable after installing a patch, but corresponding firmware updates for the embedded systems of that time are less common.
SDHC (SD 2.0)
This specification enables storage capacities of up to 32 GB under the designation SDHC (SD High Capacity) . SDHC cards do not work in devices that can only work with SD 1.0 or SD 1.1 cards; the compatibility does not necessarily have to be declared. The dimensions and contacts are the same as those of SD cards.
In addition, the SDHC specification defines performance classes that stipulate guaranteed minimum transfer rates for the recording of MPEG data streams: for class 2 cards it is 2 MB / s, for class 4 it is 4 MB / s, for class 6 it is 6 MB / s, and for class 10 it is at least 10 MB / s. AVCHD cameras usually need at least 1 MB / s, the Panasonic HDC-SD1 needs 13 MBit / s, i.e. 1.6 MB / s, which means that class 2 would be sufficient. Higher data rates are advantageous for taking serial pictures from digital cameras, provided the camera can write higher data rates and for transferring them to the PC. According to this scheme, the classes on the SDHC memory cards are printed with at least one of the numbers 2, 4, 6 or 10 within a circle open to the right (see photos). The previous SD specifications did not provide for such a standard for transfer rates that was generally binding for all manufacturers.
The first 4 GB SDHC memory card came onto the market in August 2006, followed by the world's first class 6 card with 32 GB at the beginning of 2008, followed by the class 10 cards in December 2009.
Since they are primarily intended for use in digital cameras, SDHC cards are usually formatted with the FAT32 file system . Therefore, they are not compatible with older cameras that only understand the FAT16 format (which is common with SD 1.x cards) . For use in older cameras, SDHC cards can be formatted with FAT16, but this limits the usable capacity to 2 GB and 4 GB. In principle, SD cards (and thus also SDHC cards) are not limited to the FAT file system. It is not a problem to use them with other file systems (such as UFS , ZFS , ext3 , NTFS or HFS ), which makes these media interesting because of their size as a replacement for USB sticks and for use in digital camcorders. It should be noted, however, that digital cameras cannot address them due to insufficient support for these file systems and that a card error is reported.
SDXC (SD 3.0)
At the Consumer Electronics Show 2009, the SD Card Association announced the successor to SDHC. The specification of the cards called SDXC (SD eXtended Capacity) allows a gross size of up to 2 TB (2048 GB). The division into performance classes is retained and now extends up to 104 MB / s, the plan is 300 MB / s. Technically, all file systems can be used, but for the first time the specification prescribes a specific file system, Microsoft exFAT .
Overall, exFAT has gained some popularity. Drivers for exFAT are available under Windows 7, in Windows Vista from Service Pack 1 and Mac OS X (from 10.6.5). A separate update is available for Windows XP from Service Pack 2. By means of a patent exchange agreement with Microsoft, Tuxera is in the process of developing an exFAT driver for embedded Linux. However, it is not known whether this driver, like Tuxera's NTFS-3G, will be released under the dual licensing principle under both a commercial license and an open source license.
Due to the technical and legal problems of exFAT, the ext4 driver is mostly used in Android and GNU / Linux systems . The SD card is formatted with ext2 or ext4 , depending on the application . The outdated FAT32 is still used, especially for compatibility with older devices . However, SDXC cards are only partially downward compatible with SD or SDHC readers.
On March 6, 2009, Pretec presented the first SDXC memory card with a storage capacity of 32 GB and a write and read speed of 50 MB / s. In the spring of 2010, Panasonic brought cards with 48 and 64 GB onto the market. The first card with a capacity of 128 GB was introduced by Lexar in March 2011. On September 17, 2012, Lexar announced the industry's first SDXC memory card with a total storage capacity of 256 GB. Devices that support SDXC have been available on the German market since 2010. In June 2013, PNY Technologies introduced memory cards with transfer speeds of up to 100 MB / s and sizes of up to 64 GB. On September 12, 2014, Sandisk introduced memory cards with sizes of up to 512 GB and transfer speeds of up to 95 MB / s. On September 20, 2016, Sandisk presented a prototype of a 1 TB SDXC memory card to the public at Photokina. Even before Sandisk could bring its prototype to market, Lexar presented the first 1 terabyte SD card ready for the market at CES 2019 in Las Vegas.
SDUC (SD 7.0 and SD 7.1)
Memory cards based on the SDUC ( Secure Digital Ultra Capacity ) standard can have a storage capacity between 2 and 128 terabytes . The SDUC standard was defined in 2018 and expanded for micro SD cards in 2019. The new standard also defines new data transfer speeds for SD Express and Micro-SD Express of up to 985 MB / s.
While the transmission speed was initially around 3.6 MB / s (read) and 0.8 MB / s (write), even inexpensive cards achieved a read speed of over 90 MB / s in 2019. Particularly fast SD cards with UHS-II interfaces achieved write and read speeds of around 300 MB / s each in 2019. However, the values fluctuate greatly and depend on the manufacturer and the devices used for use.
If the writing speed of memory cards is too slow, this can limit the performance of devices with a high volume of data that can be processed quickly. For example, the maximum continuous shooting speed specified for a digital still camera may not be achieved, or when recording videos, the possible resolution may be limited, dropouts may occur or the recording may be canceled. Some cameras do not allow new recordings or inputs from the operator during the write process.
The maximum possible transmission speed is often specified directly in MB / s.
Occasionally, however, especially with Lexar brand SD memory cards, the usual factors for CD burners are also used. They then refer to the single speed reading speed of CDs ; this is 150 Ki B / s. A "2000x" memory card, for example, has a write speed of 300 MiB / s.
The following speed classes are defined as minimum write speeds in the SD 5.1 specification :
|minimum sequential write speed||Speed class||application|
|2 MB / s||Class 2 (C2)||-||-||SD video recordings (up to 576)|
|4 MB / s||Class 4 (C4)||-||-||HD-ready and full HD video recordings (from 720p to 1080p / 1080i)|
|6 MB / s||Class 6 (C6)||-||Class 6 (V6)|
|10 MB / s||Class 10 (C10)||Class 1 (U1)||Class 10 (V10)||Full HD video recordings (1080p) and consecutive HD frames (High Speed Bus), real-time transmissions and large HD video files (UHS Bus)|
|30 MB / s||-||Class 3 (U3)||Class 30 (V30)||4K video files at 60/120 fps (UHS bus)|
|60 MB / s||-||-||Class 60 (V60)||8K video files with 60/120 fps (UHS bus)|
|90 MB / s||-||-||Class 90 (V90)|
|Minimum speed with random|
|Class 1 (A1)||10 MB / s||1500 IOPS||IOPS500|
|Class 2 (A2)||4000 IOPS||2000 IOPS|
On June 23, 2010, the UHS ( Ultra High Speed ) classification for the UHS bus system was presented. It is the successor to the previous Normal Bus I / F (Speed Classes 2, 4 and 6) and High Speed Bus I / F (Speed Class 10).
At the IFA 2010, the first UHS-I-SD memory cards were presented and the SD Association announced the development of SD 4.00.
On July 16, 2013 Toshiba was the first to announce SDHC and SDXC memory cards with UHS-II interface and the updated 4.10 specification. This offers a transfer rate of up to 312 MB / s, the new bus system is called UHS-II I / F and requires new contacts on the SD memory card. Nevertheless, the new standard is both upwards and downwards compatible. Cards with the additional contacts can be read and written to by older devices, but in this case they will not achieve the maximum possible speeds. As of February 2019, 27 cameras and over 50 (micro) SD memory cards with UHS-II interfaces were available.
In June 2018, SD Express was specified with a speed of up to 985 megabytes per second. For these high data rates , a third-generation PCI Express interface is also integrated into the memory cards, which can be controlled via the contacts of the UHS-II specification using the NVM Express software standard . Control via the UHS I interface is still possible, so that downward compatibility is maintained.
The microSD Express format for smartphones and other devices transfers data at up to 985 MB / s through the interfaces NVMe 1.3 and PCIe 3.1. With the low-power mode of PCIe 3.1, the cards can be operated with 1.8 instead of 3.3 volts. Such cards are marked with Lv (for low voltage ). In Lv mode, they use less power in corresponding devices than previous microSD cards.
Medium access time
The mean access time indicates the time it takes for the SD card to find a certain storage area for reading or writing. A value below 12 ms is recommended for modern systems. This is the case with almost all SD cards for read access.
Due to the storage technology used, flash memory cannot be written to an unlimited number of times. However, all cards have an algorithm through which a significantly longer usage time can be achieved. Write access to a logical block of the medium is diverted to changing physical memory areas (" wear leveling "), so that, for example, frequent writing of file system tables does not always take place on the same memory cells and can render them unusable at an early stage. However, the processes used are usually not disclosed and are rarely noted on the products, so that there is hardly any choice based on durability. The estimated service life for SLC-NAND chips is given as 1,000,000, when using MLC-NAND chips with 100,000 write operations. Read access to flash memory is unlimited.
In addition to being limited by writing processes, an SD card can also have other defects. In addition to failures due to aging, this also includes electrical damage ( ESD , often "only" the card controller fails, not the flash memory itself) and mechanical damage (damage caused by plugging, damage caused by bending the card, breaking the card).
SD cards are used in many different devices. They are often used for taking photos in digital cameras , in MP3 players for playing MP3 files, and in PDAs and cell phones for various applications. Mobile navigation systems use SD cards to store the map material, some handheld consoles and e-book readers also use SD cards, and some electronic musical instruments also use SD cards for storage.
Devices with an SD slot are usually backwards compatible with MMC cards . MMCs can usually also be operated in devices that are designed for the SD memory card. However, fast MMC cards in pure SD readers cannot be addressed at full speed; full MMC support is required for this. However, it is not possible to operate SD cards in devices that are only designed for MMC. To avoid incorrect use, SD cards have a slightly thicker casing than MMC cards. Therefore, due to their thickness, SD cards usually do not fit in MMC slots.
Apart from digital photography with high resolutions and fast image sequences or the recording of videos, the use of SD cards with a high write speed ("high speed") is not necessary for most devices and applications. SDIO-compatible slots (SDIO stands for "SD Input / Output") also enable the connection of other devices (radio, camera, W-LAN).
Tickets are sold that
- do not have the specified capacity
So that this is not noticed (immediately), the descriptor usually does not have the actual, but the alleged storage capacity. If the actual storage capacity is exceeded when saving, this is associated with the loss of all previously saved data.
- do not achieve the specified speed
Most of the time, slower cards from the manufacturer or slower cards from noname manufacturers are relabeled. The speed and reliability of the supposed model are usually not achieved.
- not from the specified manufacturer
This usually occurs in connection with the first two points.
Since the profit margin is greatest with forgeries of expensive cards, the currently fastest and / or highest capacity memory cards from well-known brand manufacturers are preferably counterfeited. Offers well below the market price from established retailers can be an indication of counterfeit products.
Target capacity and actual capacity
Counterfeit memory cards show the operating system the specified (alleged) capacity and can be formatted with the alleged capacity without a corresponding error message appearing. This is made possible by the fact that the available total memory amount (capacity) is programmed into a readable area in memory cards and other flash memories. This storage of the value of the capacity was created for the reason that it would take too long to check the capacity each time the data carrier is inserted.
When attempting to save larger amounts of data on a card manipulated in this way, as soon as the actual capacity is exhausted, all further files to be saved will no longer be saved on the SD card or will overwrite part of the data already saved. In either case, the user does not normally receive an error message, but some of the data is lost. Memory tests such as the Windows freeware program for verifying SD cards and other R / W storage media "H2testw" or the Linux command "Badblocks" or the tool for Linux "f3 - Fight Flash Fraud" indicate which ones Addresses that happen and thus enable the calculation of the actually available memory size. Because some forgeries address incorrectly, testing has to be done with a constantly changing bit pattern (random pattern).
Write / read speed
Another characteristic of a counterfeit is the actual transfer rate (write / read speed) of counterfeit memory cards, which is clearly far below the value advertised and printed on the packaging or card. The classifications of the cards (Class, UHS Class) correspond to minimum values of the sequential writing speed, whereby a significantly lower writing speed can be an indication of a forgery. However, the actual transfer speed can also be limited by other factors, such as the interface used (e.g. USB), the cable or the card reader.
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