Secure Digital
Encyclopedia
Secure Digital is a non-volatile
memory card
format developed by the SD Card Association
(SDA) for use in portable devices. The SD technology is used by more than 400 brands across dozens of product categories and more than 8,000 models, and is considered the de-facto industry standard.
Secure Digital devices comprise cards of the same physical dimensions but different communication protocols. The original, Standard-Capacity (SDSC) card family stores up to 2 GB
. The High-Capacity (SDHC) card family has a capacity of 4 GB to 32 GB. eXtended-Capacity (SDXC) card family has a capacity starting above 32 GB with a maximum of 2 TB
. The SDIO family implements input/output
functions rather than just data storage.
The current Secure Digital specifications now also comprise three different form factors: the original size, the "mini" size, and the "micro" size (see illustration). Electrically passive adaptors allow the use of a smaller card in a host device built to hold a larger card. There are many combinations of form factors and device families. SD, miniSD, and microSD are members of the SD family. SDHC, miniSDHC, and microSDHC are members of the SDHC family. SDXC and microSDXC are members of the SDXC family. SDIO and miniSDIO are members of the SDIO family.
Host devices that comply with newer versions of the specification provide backward compatibility
and accept older SD cards, but older host devices do not recognize newer cards. The existence of different families with the same physical size has confused users. In addition, some vendors have violated or creatively interpreted the SD specification to produce early, higher-capacity cards that do not work in some host devices.
, Matsushita, and Toshiba
first agreed to develop and market the SD (Secure Digital) Memory Card, which was a development of the MMC (MultiMediaCard
). With a physical profile of 32×24×2.1 mm, the new card provided both digital rights management
(DRM) up to the Secure Digital Music Initiative
(SDMI) standard, and a high memory density for the time.
The new format was designed to compete with Sony
's Memory Stick
format, which was released the prior year, and featured MagicGate
DRM. It was mistakenly predicted that DRM features would be widely used due to pressure from music and other media suppliers to prevent piracy.
The signature SD logo
was actually developed for another use entirely; it was originally used for the Super Density Disc, which was the unsuccessful Toshiba entry in the DVD
format war
. This is why the D resembles an optical disc.
At the 2000 Consumer Electronics Show
(CES) trade show Matsushita, SanDisk, and Toshiba Corporation announced the creation of the SD Card Association to promote SD cards. The association's headquarters are in California and its executive membership includes some 30 world-leading high-tech companies and major content companies. Early samples of the SD Card were available in the first quarter of 2000, with production quantities of 32 and 64 MB
cards available 3 months later.
In March 2003, SanDisk
Corporation announced the introduction of the miniSD and demonstrated it at CeBIT
2003. The miniSD card was adopted in 2003 by the SD Association as a small form factor extension to the SD card standard. While the new cards were designed especially for use in mobile phones, they are usually packaged with a miniSD adapter which enables compatibility with all devices equipped with a standard SD memory card slot.
In April 2006, the SD Association released a detailed specification for the non-security related parts of the SD memory card standard. The organization also released specifications for the Secure Digital Input Output (SDIO) cards and the standard SD host controller. During the same year, specifications were finalized for the small-form-factor microSD (formerly named TransFlash) and SDHC, with capacities in excess of 2 GB and a minimum sustained read and write speed of 17.6 Mbit/s.
In September, 2006, SanDisk announced the 4 GB miniSDHC. 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 will work with miniSD and miniSDHC, but devices without specific support for miniSDHC will work only with the older miniSD card.
In January 2009, the SD Association announced the SDXC family that will support cards up to 2 TB memory size and speeds up to 300 Mbyte/s.
, who believed current memory card formats were too large for phones. It was originally called T-Flash, but just before product launch, T-Mobile sent a cease and desist
order to SanDisk claiming they own the trademark on T-(anything) and the name was then changed to TransFlash. After pressure from Toshiba
and Panasonic
, SanDisk's partners in the 3C licensing group of the SDA, SanDisk negotiated to have the new format become a standard administered by the SD Card Association
(SDA). The SDA announced the microSD format at CTIA Wireless 2005 on March 14, 2005, and approval of the final microSD specification on July 13, 2005. At launch, the microSD format was available in capacities of 32, 64, and 128 MB. TransFlash and microSD cards are the same; each can be used in devices made for the other.
SD cards are based on the older MultiMediaCard
(MMC) format, but have a number of differences:
Devices with SD slots can use the slimmer MMCs, but standard SD cards will not fit into the slimmer MMC slots. miniSD and microSD cards can be used directly in SD slots with a simple passive adapter, since the cards differ in size and shape but not electrical interface. With an active electronic adapter, SD cards can be used in CompactFlash
or PC card
slots. Some SD cards include a USB connector for compatibility with desktop and laptop computers, and card reader
s allow SD cards to be accessed via connectivity ports such as USB, FireWire, and the parallel printer port
. SD cards can also be accessed via a floppy disk
drive with a FlashPath
adapter.
Standard size
Mini size
Micro size
On the left side there may be a write-protection notch. If this is present, the card cannot be written. If the notch is covered by a sliding write protection
tab, or absent, then the card is writeable. Because the notch is detected only by the reader, the protection can be overridden if desired (and if supported by the reader). Not all devices support write protection, which is an optional feature of the SD standard.
Some SD cards have no write-protection notch, and it is absent completely in the microSD and miniSD formats.
Some music and film media companies (e.g., Disney) have released limited catalogs of records and/or videos on SD. These usually contain DRM
-encoded Windows Media
files, making use of the SD format's DRM abilities. Such media are usually permanently marked read-only by adding the notch with no tabs.
card, an SD card of any SD family is a block-addressable
storage device
, in which the host device can read or write fixed-size blocks by specifying their block number.
MBR and FAT
Most SD cards ship preformatted with one or more MBR partitions
, where the first or only partition contains a file system
. This lets them operate like the hard disk
of a personal computer
. Typically, an SD card is formatted with MBR and the following file system:
Most consumer products that take an SD card will expect it to be partitioned and formatted in this way. The wide support for FAT16 and FAT32 lets these cards be used on virtually any host device with an SD reader, to present the user with the familiar method of named files in a hierarchical directory tree.
On such SD cards, standard utility programs such as SCANDISK
can be used to repair or retrieve corrupted data, and sometimes recover deleted files. Defragmentation
tools for FAT file systems may be used on such cards. The resulting consolidation of files may provide a marginal improvement in the time required to read or write the file, but not an improvement comparable to defragmentation of hard drives, where storing a file in multiple fragments may involve a time penalty to move between physical areas of the drive. Moreover, defragmentation performs writes to the SD card that count against the card's rated lifespan. The write endurance of the physical memory is discussed in the article on flash memory; newer technology to increase the storage capacity of a card currently provides worse write endurance.
When reformatting an SD card smaller than 4 GB, FAT16 should be used. (This is also an option for 4 GB cards, but it requires the use of 64 kiB clusters
, which are not widely supported.) FAT16 does not support cards above 4 GB.
Other file systems
Because the host views the SD card as a block storage device, the card does not require MBR partitions or any specific file system. The card can be reformatted to use any file system the operating system supports. For example:
Additionally, an SD card called Live SD can contain an embedded operating system (such as Live USB
). Computers that can bootstrap from an SD card (either using a USB adapter or inserted into the computer's flash media reader) instead of the hard disk drive may thereby be able to recover from a corrupted hard disk drive. A Live SD can be write-locked to preserve the system's integrity.
Risks of reformatting
Reformatting an SD card with a different file system, or even with the same one, may make the card slower, or shorten its lifespan. Some cards use wear leveling
, in which frequently modified blocks are mapped to different portions of memory at different times, and some wear-leveling algorithms are designed for the access patterns typical of the file allocation table on a FAT16 or FAT32 device. In addition, the preformatted file system may use a cluster size that matches the erase region of the physical memory on the card; reformatting may change the cluster size and make writes less efficient.
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 into 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.
Through issuing various commands, the host device can:
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 confining itself to use of commands supported by both standards until determining the type of card inserted, a host device can accommodate both SD and MMC cards.
Electrical interface
All SD card families initially use a 3.3-volt
electrical interface. On command, SDHC and SDXC cards switch to 1.8-volt operation.
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.
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 (DS) clock rate of up to 25 MHz. The host device is not required to use the maximum clock speed that the card supports. It may conserve power to operate at less than the maximum clock speed. Between commands, the host device can stop the clock entirely.
SDIO cards
A special family of SD cards, called SDIO, 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 a SDIO card as a "combo card" (for both memory and I/O), the host device must first select four-bit SD bus operation. The Low-Speed SDIO cards have an additional unique limit of a maximum clock rate of 400 kHz for all communications. SDIO cards support another unique feature, which is an optional interrupt output pin.
SD card pin-outs
Notes:
Ganging cards together
The one-bit SD protocol was derived from the MMC protocol, which envisaged the ability to put up to 3 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 so as to know that the host device had selected it.
The SD protocol envisaged the ability to gang 30 cards together without separate chip select lines. The host device would send commands to all cards and identify the card to respond to the command using its unique serial number.
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.
Achieving higher card speeds
The SD specification defines four-bit-wide transfers. (The MMC specification supports this and also defines an eight-bit-wide mode.) Transferring several bits on each clock pulse improves the card speed; however, the primary method that advanced SD families have used to improve speed is to switch to a faster clock frequency, once the host device verifies that the card supports the higher speed and commands it to do so.
(DRM) scheme. Roughly 10% of the storage capacity of an SD card is not available to the user, but is used by the on-card processor to verify the identity of an application program that it will then allow to read protected content. The card prohibits other accesses, such as users trying to make copies of protected files.
The DRM scheme embedded in the SD cards is the Content Protection for Recordable Media
(CPRM or CPPM) specification of the 4C Entity
, which features the Cryptomeria cipher
(also termed C2). The specification is kept secret and is accessible only to licensees. The scheme has not been broken or hacked, but this feature of SD cards is rarely actually used to protect content. DVD-Audio
uses the same DRM scheme.
Windows Phone 7
devices use SD cards designed to be accessed 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". Symbian devices, however, are some of the very few which 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.
The Super Digital cards manufactured by Super*Talent are the same in appearance and function as Secure Digital cards, but they lack the CPRM feature of Secure Digital cards.
built for a Class 6 card may suffer dropouts or corrupted video if a slower card is used. Digital camera
s may experience a noticeable lag between shots, while the camera writes the picture to a slower card.
A card's speed depends on many factors, such as the following:
In early SD cards, the speed was measured with the × rating, which compared the average speed of reading data to that of the original CD-ROM
drive. Currently, the official unit of measurement is the Speed Class Rating, which guarantees a minimum rate at which data can be written to the card.
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.
Unlike the earlier "×" speed ratings, the host device can read a card's speed class. A device can warn the user if the card reports a speed class that falls below an application's minimum need.
These are the ratings of all currently available cards:
|-
! Class !! Speed
|-
| Class 2 || 2 MB/s
|-
| Class 4 || 4 MB/s
|-
| Class 6 || 6 MB/s
|-
| Class 10 || 10 MB/s
|}
Speed Classes 2, 4, and 6 assert that the card supports the respective number of MB/s 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. By comparison, the older "×" rating measured maximum speed under ideal conditions, and was vague as to whether this was read speed or write speed.
Recent developments
On 21 May 2009, Panasonic
announced new class 10 SDHC cards, claiming that this new class is "part of SD Card Specification Ver.3.0". Toshiba also announced cards based on the new 3.0 spec.
On 1 June 2010, Pretec announced the new Class-16 HD-video grade SDXC 64 GB card at Computex Taipei 2010.
drive speed of 1.2 Mbit/s (approximately 150 kB/s). Basic cards transfer data up to six times (6×) the CD-ROM speed; that is, 7.2 Mbit/s. The 2.0 specification 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. Vendors including Transcend and Kingston
report their cards' write speed.
This table lists common ratings, the minimum transfer rates, and the corresponding Speed Class (though the comparison is not always exact).
|-
! valign="top" | Rating
! valign="top" | Read Speed
(Mbit/s)
! valign="top" | Read Speed
(MB/s)
! valign="top" | Write Speed
(Mbit/s)
! valign="top" | Write Speed
(MB/s)
! valign="top" | Speed
Class
|- style="text-align:right;"
|| 6×
|| 7.2
|| 0.9
||
||
||
|- style="text-align:right;"
|| 10×
|| 12.0
|| 1.5
||
||
||
|- style="text-align:right;"
|| 13×
|| 16.0
|| 2.0
|| 16.0
|| 2.0
|| 2
|- style="text-align:right;"
|| 26×
|| 33.0
|| 4.0
|| 32.0
|| 4.0
|| 4
|- style="text-align:right;"
|| 32×
|| 38.4
|| 4.8
|| 40.0
|| 5.0
||
|- style="text-align:right;"
|| 40×
|| 48.0
|| 6.0
|| 48.0
|| 6.0
|| 6
|- style="text-align:right;"
|| 66×
|| 80.0
|| 10.0
|| 80.0
|| 10.0
|| 10
|- style="text-align:right;"
|| 100×
|| 120.0
|| 15.0
|| 120.0
|| 15.0
||
|- style="text-align:right;"
|| 133×
|| 160.0
|| 20.0
|| 160.0
|| 20.0
||
|- style="text-align:right;"
|| 150×
|| 180.0
|| 22.5
|| 180.0
|| 22.5
||
|- style="text-align:right;"
|| 200×
|| 240.0
|| 30.0
|| 240.0
|| 30.0
||
|- style="text-align:right;"
|| 266×
|| 320.0
|| 40.0
|| 320.0
|| 40.0
||
|- style="text-align:right;"
|| 300×
|| 360.0
|| 45.0
|| 360.0
|| 45.0
||
|- style="text-align:right;"
|| 400×
|| 480.0
|| 60.0
|| 480.0
|| 60.0
||
|- style="text-align:right;"
|| 600×
|| 720.0
|| 90.0
|| 720.0
|| 90.0
||
|}
UHS memory cards work best with UHS host devices. The combination lets the user record HD resolution videos to tapeless camcorder
s while performing other functions. It is also suitable for real-time broadcasts and capturing large HD videos.
The maximum transfer rate of SDXCs that follow the SD 3.0 specification was announced to be 832 Mbit/s. (These are called UHS104 speeds.) The SD 4.0 specification is planned to increase this to 2.4 Gbit/s.
Use of UHS requires that the host device first take the following actions:
By the time the Version 2.0 (SDHC) specification was completed in June 2006, vendors had already devised 2 GB and 4 GB SD cards, either as specified in Version 1.1, or by creatively reading it, or by violating it but remaining in its framework. The resulting cards devices do not work correctly in some host devices.
In SD version 1.00, the number of bytes per block was assumed to be 512. This permitted SDSC cards up to 4,096 × 512 × 512 = 1 GB, for which there are no known incompatibilities.
Version 1.01 let an SDSC card use a 4-bit field to indicate 1,024 or 2,048 bytes per block instead. Doing so enabled cards with 2 GB and 4 GB capacity.
Early SDSC host devices that assume 512-byte blocks therefore will not fully support the insertion of 2 GB or 4 GB cards. In some cases, the host device can read data that happens to reside in the first 1 GB of the card. If the assumption is made in the driver software, success may differ from one version of Windows to another. In addition, any host device might not support a 4 GB SDSC card, since the specification lets it assume that 2 GB is the maximum for these cards.
Version 1
In CSD Version 1, capacity is calculated as follows:
Capacity=(C_SIZE+1)<<(C_SIZE_MULT+2)<
The SD Card Association specification states: "To make 2 GByte card, the Maximum Block Length (READ_BL_LENWRITE_BL_LEN) shall be set to 1024 bytes. However, the Block Length, set by CMD16, shall be up to 512 bytes to keep consistency with 512 bytes Maximum Block Length cards (Less than and equal 2 Gbyte cards)."
Version 2.0
In Version 2.0, which defines SDHC and SDXC cards, the C_SIZE portion of the CSD is 32 bits and it indicates the memory size in multiples of 512 bytes. SDHC cards are allowed to use only 26 of the 32 bits, giving a maximum size of 32 GB. In addition, the C_SIZE_MULT field is removed and the READ_BL_LEN is no longer used to compute capacity. Two bits that were formerly reserved and fixed at 0 are now called the CSD Structure and identify the card family: 0 is SDSC; 1 is high (SDHC) and extended (SDXC) capacity; 2 and 3 are reserved. Older host devices are not aware of this new field and cannot correctly identify SDHC or SDXC cards.
Capacity is calculated thus:
Capacity=(C_SIZE+1)*524288
where for SDHC 4112<=C_SIZE<=65375 (approx. 2 GB) < capacity < 32 GiB
for SDXC 65535<=C_SIZE 32 GiB <= capacity <= 2 TiB max.
Capacities above 4 GB can only be achieved by following Version 2.0. In addition, capacities equal to 4 GB must also follow Version 2.0 to guarantee compatibility.
An SDHC card could be built to report a C_SIZE value above 65375, which would indicate a capacity of over 32 GB. This would violate the Version 2.0 specification, while complying with the format of the C_SIZE field. A host device that relied on C_SIZE rather than the guarantees in the specification to determine the card's capacity might support such a card. But the card might fail in other SDHC-compatible host devices.
SDHC cards are physically and electrically identical to standard-capacity SD cards (SDSC). The major compatibility issues between SDHC and SDSC cards, as covered above, are the redefinition of the Card-Specific Data (CSD) register in Version 2.0, and the fact that SDHC cards are typically shipped preformatted with the FAT32 file system.
Host devices that accept SDHC cards are required to accept SDSC cards. However, host devices designed for SDSC do not recognize SDHC memory cards, although some devices can do so through a firmware upgrade. Microsoft Windows may need a hotfix to support accessing SDHC cards.
(CES) 2009 (January 7–10, 2009). The maximum capacity defined for SDXC cards is 2 TB
(2048 GB). The older SDHC cards also have a maximum capacity of 2 TB based on the card data structures, but this is artificially limited to 32 GB by the SD 2.0 specification. The first SDXCs being released are governed by an SD 3.0 specification (which also still specifies FAT32 and thus lower capacities), whereas higher capacity and faster SDXCs are expected to follow an SD 4.0 specification, which was formally announced in January 2011.
The SDcard association selected Microsoft
's proprietary exFAT
file system in the official SDXC specification; however, as with SD and SDHC, it is still a plain block device
and thus arbitrary partitioning and other file systems can be used, such as btrFS
, ext4
, HFS Plus
, NTFS
, UFS
, etc.
and Sony
announced the joint development of the XC variant of the competing Memory Stick
format, boasting the same 2 TB maximum capacity of SDXC.
On January 8, 2009, Panasonic
announced plans for production of 64 GB SDXC cards.
On March 6, 2009, Pretec introduced the world's first SDXC card with a capacity of 32 GB and a read/write speed of 400 Mbit/s. At the introduction, there were no products compatible with the new memory card.
On August 3, 2009, Toshiba
announced it will launch the world's first 64 GB SDXC Memory Card with a read speed of 480 Mbit
/s. The 64 GB card (THNSU064GAA2BC) was planned to be available in the spring of 2010. Toshiba card was available from April 13.
On January 6, 2010, Panasonic
announced its first SDXC cards with 64 GB and 48 GB to be available in February (RP-SDW64GE1K and RP-SDW48GE1K).
On January 6, 2010, Sony
announced the launch of Handycam HDR-CX55V with SDXC support.
On February 8, 2010, Canon announced the launch of the new EOS Rebel T2i
Digital SLR camera, the first EOS model to support SDXC memory cards.
On February 19, 2010, Panasonic
launched in Japan World's first available for consumers SDXC memory cards with 64 GB and 48 GB (RP-SDW64GE1K and RP-SDW48GE1K) together with USB card readers compatible with SDXC format.
On February 22, 2010, SanDisk
launched its 64 GB SanDisk Ultra SDXC card.
The first integrated SDXC card readers are available from JMicron and are expected to be used in laptops in 2010.
In January, 2011, Centon Electronics, Inc.
began shipping its 64 GB and 128 GB Class 10 SDXC card.
In March, 2011, Lexar
began shipping its 128 GB Class 10 SDXC card.
In September 2011, a 64 GB microSDXC card was released by SanDisk
filesystem, are compatible with SDXC cards. The decision to label cards with a capacity greater than 32 GB as SDXC and to use a different filesystem is due solely to the limitations in creating larger filesystems in certain versions of Microsoft Windows. Other operating system kernels, such as Linux, make no distinction between SDHC and SDXC cards, as long as the card contains a compatible filesystem.
SDHC and SDXC cards and hosts have these compatibility issues:
s, barcode reader
s, FM radio tuners, TV tuners, RFID readers, digital camera
s, 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 8 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.
Host support for SDIO
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. (Bluetooth devices exhibit comparable compatibility issues, although to a lesser extent thanks to standardized Bluetooth profiles.)
Devices such as netbooks, digital camera
s, camcorder
s, personal digital assistant
(PDAs), mobile phone
s, video game console
s, digital audio players, and many others use them.
Smaller devices tend to use microSD or miniSD rather than full sized SD cards.
SD cards are not generally used in mass produced devices where only a small amount of storage is needed due to economic reasons, or where a very large amount of storage is needed.
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, with cards not being easily available in 2007.
At this time all the leading digital camera manufacturers use 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 Card
s (xD cards) exclusively, while Sony
only used Memory Stick
; however , all three support SD.
Some prosumer
and professional digital camera
models continue to offer CompactFlash
, either on a second card slot or as the only storage, as it has historically offered a better price/capacity ratio and faster transfer rates.
Secure Digital memory cards can be used in Sony XDCAM
EX camcorder
s via the MEAD-SD01 adapter.
s accommodate SD cards as an auxiliary storage device through a built-in slot or a USB adaptor, SD cards cannot be used as the primary hard disk
because none of the SD card variants supports ATA signaling. This use requires a separate SD controller chip or a SD-to-CompactFlash converter.
Most modern microcontroller
s have built-in SPI
logic that can interface to a 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 Linksys
WRT54G
router with MMC support code from the Linux kernel
. This technique can achieve throughput of up to .
s and trademark
s. Three versions of the SD specification have been set: 1.0, 1.1 and 2.0. These were originally available only after agreeing to a non-disclosure agreement
(NDA) that prohibited development of an open source
driver, which generated consternation in the open-source and free software
communities. However, the system was eventually reverse-engineered, and the non-DRMed sections of the memory cards could be accessed by free software drivers. Since then, the SD Card Association
(SDA) has made access to a simplified version of the specification available under a less restrictive license. Although most open-source drivers were written before this, it has helped them to solve some compatibility issues.
In 2006, the SD Card Association also released a simplified version of their host controller interface specification (not to be confused with the physical specification, which covers the actual cards and their protocol) and later also for physical layer, ASSD extensions, SDIO
and SDIO
Bluetooth
Type-A specifications under a disclaimers agreement. Like the physical specification, most of the information had already been discovered before the public release and at least Linux
had a fully free driver for it. Still, building a chip conforming to this specification caused the One Laptop per Child project to claim "the first truly Open Source SD implementation, with no need to obtain an SDI license or sign NDAs to create SD drivers or applications."
For the most part, the lack of a complete, open SD specification mainly affects embedded system
s and laptop systems, since desktop users generally read SD cards via USB-based card readers. These card readers present a standard USB mass storage interface to memory cards, thus separating the operating system from the details of the underlying SD interface. However, embedded systems (such as portable music players) usually access SD cards directly, and therefore complete programming information is necessary. Desktop card readers are themselves examples of such embedded systems; the manufacturers of these readers have usually paid the SDCA for complete access to the SD specifications. Many notebook computers now include SD card readers not based on USB; device drivers for these essentially access the SD card directly, as in embedded systems.
Royalties for SD card licences are imposed for manufacture and sale of memory cards and host adapters (USD$1,000/year plus membership at USD$1,500/year) but SDIO cards can be made without royalties and MMC host adapters do not require a royalty. MMCs have a seven-pin interface; SD and SDIO have expanded this to nine pins and MMC Plus expands this even further with thirteen pins.
or USB flash memory drives
; these are open standard
s which can be implemented free of payment for licensing, royalties, or documentation. (CompactFlash and USB flash drives may, however, require licensing fees for the use of associated logo
s and trademark
s.)
However, SD is much more open than Memory Stick
, for which no public documentation nor any documented legacy implementation is available. All SD cards can be accessed freely using the well-documented SPI
bus.
xD
cards are simply 18-pin NAND flash chips in a special package and support the standard command set for raw NAND flash access. Although the raw hardware interface to xD cards is well understood, the layout of its memory contents—necessary for interoperability with xD card readers and digital cameras—is totally undocumented. The consortium that licenses xD cards has not released any technical information to the public.
Specifications
Software
Comparisons
Interfacing
Non-volatile memory
Non-volatile memory, nonvolatile memory, NVM or non-volatile storage, in the most basic sense, is computer memory that can retain the stored information even when not powered. Examples of non-volatile memory include read-only memory, flash memory, ferroelectric RAM, most types of magnetic computer...
memory card
Memory card
A memory card or flash card is an electronic flash memory data storage device used for storing digital information. They are commonly used in many electronic devices, including digital cameras, mobile phones, laptop computers, MP3 players, and video game consoles...
format developed by the SD Card Association
SD Card Association
The SD Card Association develops and publishes technical standards for SD Card technology, and promotes the use of the technology. SD Cards are compact data storage devices used to store digital files, such as picture files recorded by digital cameras. The association was founded on 28 January...
(SDA) for use in portable devices. The SD technology is used by more than 400 brands across dozens of product categories and more than 8,000 models, and is considered the de-facto industry standard.
Secure Digital devices comprise cards of the same physical dimensions but different communication protocols. The original, Standard-Capacity (SDSC) card family stores up to 2 GB
Gigabyte
The gigabyte is a multiple of the unit byte for digital information storage. The prefix giga means 109 in the International System of Units , therefore 1 gigabyte is...
. The High-Capacity (SDHC) card family has a capacity of 4 GB to 32 GB. eXtended-Capacity (SDXC) card family has a capacity starting above 32 GB with a maximum of 2 TB
Terabyte
The terabyte is a multiple of the unit byte for digital information. The prefix tera means 1012 in the International System of Units , and therefore 1 terabyte is , or 1 trillion bytes, or 1000 gigabytes. 1 terabyte in binary prefixes is 0.9095 tebibytes, or 931.32 gibibytes...
. The SDIO family implements input/output
Input/output
In computing, input/output, or I/O, refers to the communication between an information processing system , and the outside world, possibly a human, or another information processing system. Inputs are the signals or data received by the system, and outputs are the signals or data sent from it...
functions rather than just data storage.
The current Secure Digital specifications now also comprise three different form factors: the original size, the "mini" size, and the "micro" size (see illustration). Electrically passive adaptors allow the use of a smaller card in a host device built to hold a larger card. There are many combinations of form factors and device families. SD, miniSD, and microSD are members of the SD family. SDHC, miniSDHC, and microSDHC are members of the SDHC family. SDXC and microSDXC are members of the SDXC family. SDIO and miniSDIO are members of the SDIO family.
Host devices that comply with newer versions of the specification provide backward compatibility
Backward compatibility
In the context of telecommunications and computing, a device or technology is said to be backward or downward compatible if it can work with input generated by an older device...
and accept older SD cards, but older host devices do not recognize newer cards. The existence of different families with the same physical size has confused users. In addition, some vendors have violated or creatively interpreted the SD specification to produce early, higher-capacity cards that do not work in some host devices.
History
In 1999, SanDiskSanDisk
SanDisk Corporation is an American multinational corporation that designs, develops and manufactures data storage solutions in a range of form factors using the flash memory, controller and firmware technologies. It was founded in 1988 by Dr. Eli Harari and Sanjay Mehrotra, non-volatile memory...
, Matsushita, and Toshiba
Toshiba
is a multinational electronics and electrical equipment corporation headquartered in Tokyo, Japan. It is a diversified manufacturer and marketer of electrical products, spanning information & communications equipment and systems, Internet-based solutions and services, electronic components and...
first agreed to develop and market the SD (Secure Digital) Memory Card, which was a development of the MMC (MultiMediaCard
MultiMediaCard
The MultiMediaCard is a flash memory memory card standard. Unveiled in 1997 by Siemens AG and SanDisk, it is based on Toshiba's NAND-based flash memory, and is therefore much smaller than earlier systems based on Intel NOR-based memory such as CompactFlash. MMC is about the size of a postage...
). With a physical profile of 32×24×2.1 mm, the new card provided both digital rights management
Digital rights management
Digital rights management is a class of access control technologies that are used by hardware manufacturers, publishers, copyright holders and individuals with the intent to limit the use of digital content and devices after sale. DRM is any technology that inhibits uses of digital content that...
(DRM) up to the Secure Digital Music Initiative
Secure Digital Music Initiative
Secure Digital Music Initiative was a forum formed in late 1998, composed of more than 200 IT, consumer electronics, security technology, ISP and recording industry companies, ostensibly with the purpose of developing technology specifications that protected the playing, storing and distributing...
(SDMI) standard, and a high memory density for the time.
The new format was designed to compete with Sony
Sony
, commonly referred to as Sony, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan and the world's fifth largest media conglomerate measured by revenues....
's Memory Stick
Memory Stick
Memory Stick is a removable flash memory card format, launched by Sony in October 1998, and is also used in general to describe the whole family of Memory Sticks...
format, which was released the prior year, and featured MagicGate
MagicGate
MagicGate is a copy-protection technology introduced by Sony in 1999 as part of the Secure Digital Music Initiative . It works by encrypting the content on the device and using MagicGate chips in both the storage device and the reader to enforce control over how files are copied.MagicGate...
DRM. It was mistakenly predicted that DRM features would be widely used due to pressure from music and other media suppliers to prevent piracy.
The signature SD logo
Logo
A logo is a graphic mark or emblem commonly used by commercial enterprises, organizations and even individuals to aid and promote instant public recognition...
was actually developed for another use entirely; it was originally used for the Super Density Disc, which was the unsuccessful Toshiba entry in the DVD
DVD
A DVD is an optical disc storage media format, invented and developed by Philips, Sony, Toshiba, and Panasonic in 1995. DVDs offer higher storage capacity than Compact Discs while having the same dimensions....
format war
Format war
A format war describes competition between mutually incompatible proprietary formats that compete for the same market, typically for data storage devices and recording formats for electronic media. It is often characterized by political and financial influence on content publishers by the...
. This is why the D resembles an optical disc.
At the 2000 Consumer Electronics Show
Consumer Electronics Show
The International Consumer Electronics Show is a major technology-related trade show held each January in the Las Vegas Convention Center, Las Vegas, Nevada, United States. Not open to the public, the Consumer Electronics Association-sponsored show typically hosts previews of products and new...
(CES) trade show Matsushita, SanDisk, and Toshiba Corporation announced the creation of the SD Card Association to promote SD cards. The association's headquarters are in California and its executive membership includes some 30 world-leading high-tech companies and major content companies. Early samples of the SD Card were available in the first quarter of 2000, with production quantities of 32 and 64 MB
Megabyte
The megabyte is a multiple of the unit byte for digital information storage or transmission with two different values depending on context: bytes generally for computer memory; and one million bytes generally for computer storage. The IEEE Standards Board has decided that "Mega will mean 1 000...
cards available 3 months later.
In March 2003, SanDisk
SanDisk
SanDisk Corporation is an American multinational corporation that designs, develops and manufactures data storage solutions in a range of form factors using the flash memory, controller and firmware technologies. It was founded in 1988 by Dr. Eli Harari and Sanjay Mehrotra, non-volatile memory...
Corporation announced the introduction of the miniSD and demonstrated it at CeBIT
CeBIT
CeBIT is the world's largest and most international computer expo. CeBIT is held each year on the world's largest fairground in Hanover, Germany, and is a barometer of the state of the art in information technology...
2003. The miniSD card was adopted in 2003 by the SD Association as a small form factor extension to the SD card standard. While the new cards were designed especially for use in mobile phones, they are usually packaged with a miniSD adapter which enables compatibility with all devices equipped with a standard SD memory card slot.
In April 2006, the SD Association released a detailed specification for the non-security related parts of the SD memory card standard. The organization also released specifications for the Secure Digital Input Output (SDIO) cards and the standard SD host controller. During the same year, specifications were finalized for the small-form-factor microSD (formerly named TransFlash) and SDHC, with capacities in excess of 2 GB and a minimum sustained read and write speed of 17.6 Mbit/s.
In September, 2006, SanDisk announced the 4 GB miniSDHC. 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 will work with miniSD and miniSDHC, but devices without specific support for miniSDHC will work only with the older miniSD card.
In January 2009, the SD Association announced the SDXC family that will support cards up to 2 TB memory size and speeds up to 300 Mbyte/s.
microSD
The microSD format was created by SanDisk. The concept was the brainchild of the CTOs of SanDisk and of MotorolaMotorola
Motorola, Inc. was an American multinational telecommunications company based in Schaumburg, Illinois, which was eventually divided into two independent public companies, Motorola Mobility and Motorola Solutions on January 4, 2011, after losing $4.3 billion from 2007 to 2009...
, who believed current memory card formats were too large for phones. It was originally called T-Flash, but just before product launch, T-Mobile sent a cease and desist
Cease and desist
A cease and desist is an order or request to halt an activity and not to take it up again later or else face legal action. The recipient of the cease-and-desist may be an individual or an organization....
order to SanDisk claiming they own the trademark on T-(anything) and the name was then changed to TransFlash. After pressure from Toshiba
Toshiba
is a multinational electronics and electrical equipment corporation headquartered in Tokyo, Japan. It is a diversified manufacturer and marketer of electrical products, spanning information & communications equipment and systems, Internet-based solutions and services, electronic components and...
and Panasonic
Panasonic
Panasonic is an international brand name for Japanese electric products manufacturer Panasonic Corporation, which was formerly known as Matsushita Electric Industrial Co., Ltd...
, SanDisk's partners in the 3C licensing group of the SDA, SanDisk negotiated to have the new format become a standard administered by the SD Card Association
SD Card Association
The SD Card Association develops and publishes technical standards for SD Card technology, and promotes the use of the technology. SD Cards are compact data storage devices used to store digital files, such as picture files recorded by digital cameras. The association was founded on 28 January...
(SDA). The SDA announced the microSD format at CTIA Wireless 2005 on March 14, 2005, and approval of the final microSD specification on July 13, 2005. At launch, the microSD format was available in capacities of 32, 64, and 128 MB. TransFlash and microSD cards are the same; each can be used in devices made for the other.
Design and implementation
MultiMediaCard
The MultiMediaCard is a flash memory memory card standard. Unveiled in 1997 by Siemens AG and SanDisk, it is based on Toshiba's NAND-based flash memory, and is therefore much smaller than earlier systems based on Intel NOR-based memory such as CompactFlash. MMC is about the size of a postage...
(MMC) format, but have a number of differences:
- The SD card is asymmetrically shaped to prevent inserting it upside down, while an MMC will go in most of the way but make no contact if inverted.
- SD cards are thicker than MMCs. SD cards generally measure 32 × 24 × 2.1 mm, but as with MMCs can be as slim as 1.4 mm if they lack a write-protect switch; such cards, called Thin SD, are described in the SD specification, but they are non-existent or rare in the market as most devices requiring a slimmer card use the smaller versions of SD: miniSD or microSD.
- The card's electrical contacts are recessed beneath the surface of the card, protecting them from contact with a user's fingers.
- SD cards typically have transfer rates in the range of 80–160 Mbit/s, but this is likely to grow, due to recent improvements to the MMC standard.
Devices with SD slots can use the slimmer MMCs, but standard SD cards will not fit into the slimmer MMC slots. miniSD and microSD cards can be used directly in SD slots with a simple passive adapter, since the cards differ in size and shape but not electrical interface. With an active electronic adapter, SD cards can be used in CompactFlash
CompactFlash
CompactFlash is a mass storage device format used in portable electronic devices. Most CompactFlash devices contain flash memory in a standardized enclosure. The format was first specified and produced by SanDisk in 1994...
or PC card
PC card
In computing, PC Card is the form factor of a peripheral interface designed for laptop computers. The PC Card standard was defined and developed by the Personal Computer Memory Card International Association which itself was created by a number of computer industry companies in the United States...
slots. Some SD cards include a USB connector for compatibility with desktop and laptop computers, and card reader
Card reader
A card reader is a data input device that reads data from a card-shaped storage medium. Historically, paper or cardboard punched cards were used throughout the first several decades of the computer industry to store information and programs for computer system, and were read by punched card readers...
s allow SD cards to be accessed via connectivity ports such as USB, FireWire, and the parallel printer port
Parallel port
A parallel port is a type of interface found on computers for connecting various peripherals. In computing, a parallel port is a parallel communication physical interface. It is also known as a printer port or Centronics port...
. SD cards can also be accessed via a floppy disk
Floppy disk
A floppy disk is a disk storage medium composed of a disk of thin and flexible magnetic storage medium, sealed in a rectangular plastic carrier lined with fabric that removes dust particles...
drive with a FlashPath
FlashPath
FlashPath were a series of devices produced by SanDisk that allowed a variety of memory cards to be used in a 3.5" Floppy disk drive. The initial version introduced in May 1998 allowed SmartMedia cards to be used with a floppy drive. Later, Memory Stick and Secure Digital/Multi Media Card versions...
adapter.
Physical size
Each SD card family is available in up to three physical sizes. The SD and SDHC families are available in all three sizes, but the SDXC family is not available in the mini size, and the SDIO family is not available in the micro size.Standard size
- SD, SDHC, SDXC, SDIO
- 32 mm × 24 mm × 2.1 mm; the MMC and rare thin SD cards are 1.4 mm thick.
Mini size
- miniSD, miniSDHC, miniSDIO
- 21.5 mm × 20 mm × 1.4 mm
Micro size
- microSD, microSDHC, microSDXC
- 15 mm × 11 mm × 1.0 mm
Optional write-protect tab
When looking at the card from the top (see pictures) there is one required notch on the right side, the side with the diagonal cut-off corner.On the left side there may be a write-protection notch. If this is present, the card cannot be written. If the notch is covered by a sliding write protection
Write protection
Write protection is any physical mechanism that prevents modification or erasure of valuable data on a device. Most commercial software, audio and video is sold pre-protected.-Examples:...
tab, or absent, then the card is writeable. Because the notch is detected only by the reader, the protection can be overridden if desired (and if supported by the reader). Not all devices support write protection, which is an optional feature of the SD standard.
Some SD cards have no write-protection notch, and it is absent completely in the microSD and miniSD formats.
Some music and film media companies (e.g., Disney) have released limited catalogs of records and/or videos on SD. These usually contain DRM
Digital rights management
Digital rights management is a class of access control technologies that are used by hardware manufacturers, publishers, copyright holders and individuals with the intent to limit the use of digital content and devices after sale. DRM is any technology that inhibits uses of digital content that...
-encoded Windows Media
Windows Media
Windows Media is a multimedia framework for media creation and distribution for Microsoft Windows. It consists of a software development kit with several application programming interfaces and a number of prebuilt technologies, and is the replacement of NetShow technologies.The Windows Media SDK...
files, making use of the SD format's DRM abilities. Such media are usually permanently marked read-only by adding the notch with no tabs.
File system
Like other types of flash memoryFlash memory
Flash memory is a non-volatile computer storage chip that can be electrically erased and reprogrammed. It was developed from EEPROM and must be erased in fairly large blocks before these can be rewritten with new data...
card, an SD card of any SD family is a block-addressable
Block (data storage)
In computing , a block is a sequence of bytes or bits, having a nominal length . Data thus structured are said to be blocked. The process of putting data into blocks is called blocking. Blocking is used to facilitate the handling of the data-stream by the computer program receiving the data...
storage device
Storage device
Storage device may refer to:*Box, or any of a variety of containers or receptacles*Data storage device, a device for recording information, which could range from handwriting to video or acoustic recording, or to electromagnetic energy modulating magnetic tape and optical discs* Object storage...
, in which the host device can read or write fixed-size blocks by specifying their block number.
MBR and FAT
Most SD cards ship preformatted with one or more MBR partitions
Master boot record
A master boot record is a type of boot sector popularized by the IBM Personal Computer. It consists of a sequence of 512 bytes located at the first sector of a data storage device such as a hard disk...
, where the first or only partition contains a file system
File system
A file system is a means to organize data expected to be retained after a program terminates by providing procedures to store, retrieve and update data, as well as manage the available space on the device which contain it. A file system organizes data in an efficient manner and is tuned to the...
. This lets them operate like the hard disk
Hard disk
A hard disk drive is a non-volatile, random access digital magnetic data storage device. It features rotating rigid platters on a motor-driven spindle within a protective enclosure. Data is magnetically read from and written to the platter by read/write heads that float on a film of air above the...
of a personal computer
Personal computer
A personal computer is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end-user with no intervening computer operator...
. Typically, an SD card is formatted with MBR and the following file system:
- For SDSC cards: FAT16File Allocation TableFile Allocation Table is a computer file system architecture now widely used on many computer systems and most memory cards, such as those used with digital cameras. FAT file systems are commonly found on floppy disks, flash memory cards, digital cameras, and many other portable devices because of...
- For SDHC cards: FAT32
- For SDXC cards: exFATExFATexFAT is a proprietary, patent-pending file system designed especially for USB flash drives. Developed by Microsoft, it is supported in Windows XP and Windows Server 2003 with update KB955704, Windows Embedded CE 6.0, Windows Vista with Service Pack 1, Windows Server 2008, Windows 7, Windows...
.
Most consumer products that take an SD card will expect it to be partitioned and formatted in this way. The wide support for FAT16 and FAT32 lets these cards be used on virtually any host device with an SD reader, to present the user with the familiar method of named files in a hierarchical directory tree.
On such SD cards, standard utility programs such as SCANDISK
SCANDISK
SCANDISK or ScanDisk is a utility in MS-DOS and Microsoft Windows systems which checks and repairs file systems and bad clusters on the hard drive. It was introduced in MS-DOS version 6.2...
can be used to repair or retrieve corrupted data, and sometimes recover deleted files. Defragmentation
Defragmentation
In the maintenance of file systems, defragmentation is a process that reduces the amount of fragmentation. It does this by physically organizing the contents of the mass storage device used to store files into the smallest number of contiguous regions . It also attempts to create larger regions of...
tools for FAT file systems may be used on such cards. The resulting consolidation of files may provide a marginal improvement in the time required to read or write the file, but not an improvement comparable to defragmentation of hard drives, where storing a file in multiple fragments may involve a time penalty to move between physical areas of the drive. Moreover, defragmentation performs writes to the SD card that count against the card's rated lifespan. The write endurance of the physical memory is discussed in the article on flash memory; newer technology to increase the storage capacity of a card currently provides worse write endurance.
When reformatting an SD card smaller than 4 GB, FAT16 should be used. (This is also an option for 4 GB cards, but it requires the use of 64 kiB clusters
Cluster (file system)
In computer file systems, a cluster or allocation unit is the unit of disk space allocation for files and directories. To reduce the overhead of managing on-disk data structures, the filesystem does not allocate individual disk sectors, but contiguous groups of sectors, called clusters.On a disk...
, which are not widely supported.) FAT16 does not support cards above 4 GB.
Other file systems
Because the host views the SD card as a block storage device, the card does not require MBR partitions or any specific file system. The card can be reformatted to use any file system the operating system supports. For example:
- Under Unix-likeUnix-likeA Unix-like operating system is one that behaves in a manner similar to a Unix system, while not necessarily conforming to or being certified to any version of the Single UNIX Specification....
operating systems such as LinuxLinuxLinux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
or FreeBSDFreeBSDFreeBSD is a free Unix-like operating system descended from AT&T UNIX via BSD UNIX. Although for legal reasons FreeBSD cannot be called “UNIX”, as the direct descendant of BSD UNIX , FreeBSD’s internals and system APIs are UNIX-compliant...
, SD cards can be formatted using the UFSUnix File SystemThe Unix file system is a file system used by many Unix and Unix-like operating systems. It is also called the Berkeley Fast File System, the BSD Fast File System or FFS...
, EXT3 or the ReiserFS file systems. - Under Mac OS XMac OS XMac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...
, SD cards can be partitioned as GUIDGUID Partition TableIn computer hardware, GUID Partition Table is a standard for the layout of the partition table on a physical hard disk. Although it forms a part of the Extensible Firmware Interface standard , it is also used on some BIOS systems because of the limitations of MBR partition tables, which restrict...
devices and formatted with the HFS PlusHFS PlusHFS Plus or HFS+ is a file system developed by Apple Inc. to replace their Hierarchical File System as the primary file system used in Macintosh computers . It is also one of the formats used by the iPod digital music player...
file system. - Under WindowsMicrosoft WindowsMicrosoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
and some Unix systems, SD cards can be formatted using NTFSNTFSNTFS is the standard file system of Windows NT, including its later versions Windows 2000, Windows XP, Windows Server 2003, Windows Server 2008, Windows Vista, and Windows 7....
and, on later versions, exFATExFATexFAT is a proprietary, patent-pending file system designed especially for USB flash drives. Developed by Microsoft, it is supported in Windows XP and Windows Server 2003 with update KB955704, Windows Embedded CE 6.0, Windows Vista with Service Pack 1, Windows Server 2008, Windows 7, Windows...
.
Additionally, an SD card called Live SD can contain an embedded operating system (such as Live USB
Live USB
A live USB is a USB flash drive or a USB external hard disk drive containing a full operating system that can be booted. Live USBs are closely related to live CDs, but sometimes have the ability to persistently save settings and permanently install software packages back onto the USB device...
). Computers that can bootstrap from an SD card (either using a USB adapter or inserted into the computer's flash media reader) instead of the hard disk drive may thereby be able to recover from a corrupted hard disk drive. A Live SD can be write-locked to preserve the system's integrity.
Risks of reformatting
Reformatting an SD card with a different file system, or even with the same one, may make the card slower, or shorten its lifespan. Some cards use wear leveling
Wear leveling
Wear leveling is a technique for prolonging the service life of some kinds of erasable computer storage media, such as Flash memory used in solid-state drives and USB Flash drives...
, in which frequently modified blocks are mapped to different portions of memory at different times, and some wear-leveling algorithms are designed for the access patterns typical of the file allocation table on a FAT16 or FAT32 device. In addition, the preformatted file system may use a cluster size that matches the erase region of the physical memory on the card; reformatting may change the cluster size and make writes less efficient.
Transfer modes
Various SD cards may support various combinations of the following bus types and transfer modes. The SPI bus and one-bit SD bus are mandatory for all SD families, as explained in the next section.- SPI: Serial Peripheral Interface BusSerial Peripheral Interface BusThe Serial Peripheral Interface Bus or SPI bus is a synchronous serial data link standard named by Motorola that operates in full duplex mode. Devices communicate in master/slave mode where the master device initiates the data frame. Multiple slave devices are allowed with individual slave select ...
is primarily used by embedded microcontrollerMicrocontrollerA microcontroller is a small computer on a single integrated circuit containing a processor core, memory, and programmable input/output peripherals. Program memory in the form of NOR flash or OTP ROM is also often included on chip, as well as a typically small amount of RAM...
s. This bus type supports only a 3.3-volt interface. - One-bit SD: Separate command and data channels and a proprietary transfer format.
- Four-bit SD: Uses extra pins plus some reassigned pins. UHS-I and UHS-II requires this bus type.
Interface
Command interfaceSD cards and host devices initially communicate through a synchronous one-bit interface, where the host device provides a clock signal that strobes single bits into 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.
Through issuing various commands, the host device can:
- 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
MultiMediaCard
The MultiMediaCard is a flash memory memory card standard. Unveiled in 1997 by Siemens AG and SanDisk, it is based on Toshiba's NAND-based flash memory, and is therefore much smaller than earlier systems based on Intel NOR-based memory such as CompactFlash. MMC is about the size of a postage...
(MMC) interface. SD cards dropped support for some of the commands in the MMC protocol, but added commands related to copy protection. By confining itself to use of commands supported by both standards until determining the type of card inserted, a host device can accommodate both SD and MMC cards.
Electrical interface
All SD card families initially use a 3.3-volt
Volt
The volt is the SI derived unit for electric potential, electric potential difference, and electromotive force. The volt is named in honor of the Italian physicist Alessandro Volta , who invented the voltaic pile, possibly the first chemical battery.- Definition :A single volt is defined as the...
electrical interface. On command, SDHC and SDXC cards switch to 1.8-volt operation.
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.
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 (DS) clock rate of up to 25 MHz. The host device is not required to use the maximum clock speed that the card supports. It may conserve power to operate at less than the maximum clock speed. Between commands, the host device can stop the clock entirely.
SDIO cards
A special family of SD cards, called SDIO, 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 a SDIO card as a "combo card" (for both memory and I/O), the host device must first select four-bit SD bus operation. The Low-Speed SDIO cards have an additional unique limit of a maximum clock rate of 400 kHz for all communications. SDIO cards support another unique feature, which is an optional interrupt output pin.
SD card pin-outs
| Pin | Name | I/O | Logic | Description |
|---|---|---|---|---|
| 1 | nCS | I | PP | Card Select (Neg True) |
| 2 | DI | I | PP | Data In [MOSI] |
| 3 | VSS | S | S | Ground |
| 4 | VDD | S | S | Power |
| 5 | CLK | I | PP | Clock [SCLK] |
| 6 | VSS | S | S | Ground |
| 7 | DO | O | PP | Data Out [MISO] |
| 8 | NC nIRQ |
. O |
. OD |
NC (Memory Cards) Interrupt (SDIO Cards) |
| 9 | NC | . | . | NC |
| Pin | Name | I/O | Logic | Description |
|---|---|---|---|---|
| 1 | NC | . | . | NC |
| 2 | CMD | I/O | PP,OD | Command, Response |
| 3 | VSS | S | S | Ground |
| 4 | VDD | S | S | Power |
| 5 | CLK | I | PP | Clock |
| 6 | VSS | S | S | Ground |
| 7 | DAT0 | I/O | PP | Data 0 |
| 8 | NC nIRQ |
. O |
. OD |
NC (Memory Cards) Interrupt (SDIO Cards) |
| 9 | NC | . | . | NC |
| Pin | Name | I/O | Logic | Description |
|---|---|---|---|---|
| 1 | DAT3 | I/O | PP | Data 3 |
| 2 | CMD | I/O | PP,OD | Command, Response |
| 3 | VSS | S | S | Ground |
| 4 | VDD | S | S | Power |
| 5 | CLK | I | PP | Clock |
| 6 | VSS | S | S | Ground |
| 7 | DAT0 | I/O | PP | Data 0 |
| 8 | DAT1 nIRQ |
I/O O |
PP OD |
Data 1. SDIO Cards share with Interrupt Period |
| 9 | DAT2 | I/O | PP | Data 2 |
Notes:
- Direction is relative to card. I = Input, O = Output.
- PP = Push-Pull logic, OD = Open-DrainOpen collectorAn open collector is a common type of output found on many integrated circuits . Instead of outputting a signal of a specific voltage or current, the output signal is applied to the base of an internal NPN transistor whose collector is externalized on a pin of the IC. The emitter of the...
logic. - S = Power SupplyIC power supply pinAlmost all integrated circuits have at least two pins that connect to the power rails of the circuit in which they are installed. These are known as the IC's power supply pins...
, NC = Not Connected (or logical highPull-up resistorPull-up resistors are used in electronic logic circuits to ensure that inputs to logic systems settle at expected logic levels if external devices are disconnected or high-impedance...
).
Ganging cards together
The one-bit SD protocol was derived from the MMC protocol, which envisaged the ability to put up to 3 cards on a bus of common signal lines. The cards use open collector
Open collector
An open collector is a common type of output found on many integrated circuits . Instead of outputting a signal of a specific voltage or current, the output signal is applied to the base of an internal NPN transistor whose collector is externalized on a pin of the IC. The emitter of the...
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
Pull-up resistor
Pull-up resistors are used in electronic logic circuits to ensure that inputs to logic systems settle at expected logic levels if external devices are disconnected or high-impedance...
) if no card pulls it low. Though the cards shared clock and signal lines, each card had its own chip select
Chip select
Chip select or slave select is the name of a control line in digital electronics used to select one chip out of several connected to the same computer bus usually utilizing the three-state logic....
line so as to know that the host device had selected it.
The SD protocol envisaged the ability to gang 30 cards together without separate chip select lines. The host device would send commands to all cards and identify the card to respond to the command using its unique serial number.
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.
Achieving higher card speeds
The SD specification defines four-bit-wide transfers. (The MMC specification supports this and also defines an eight-bit-wide mode.) Transferring several bits on each clock pulse improves the card speed; however, the primary method that advanced SD families have used to improve speed is to switch to a faster clock frequency, once the host device verifies that the card supports the higher speed and commands it to do so.
DRM features
All SD cards incorporate a digital rights managementDigital rights management
Digital rights management is a class of access control technologies that are used by hardware manufacturers, publishers, copyright holders and individuals with the intent to limit the use of digital content and devices after sale. DRM is any technology that inhibits uses of digital content that...
(DRM) scheme. Roughly 10% of the storage capacity of an SD card is not available to the user, but is used by the on-card processor to verify the identity of an application program that it will then allow to read protected content. The card prohibits other accesses, such as users trying to make copies of protected files.
The DRM scheme embedded in the SD cards is the Content Protection for Recordable Media
Content Protection for Recordable Media
Content Protection for Recordable Media and Pre-Recorded Media is a mechanism for controlling the copying, moving and deletion of digital media on a host device, such as a personal computer, or other digital player...
(CPRM or CPPM) specification of the 4C Entity
4C Entity
The 4C Entity is a consortium formed by IBM, Intel, Matsushita and Toshiba to establish a common platform for digital rights management schemes...
, which features the Cryptomeria cipher
Cryptomeria cipher
The Cryptomeria cipher, also called C2, is a proprietary block cipher defined and licensed by the 4C Entity. It is the successor to CSS algorithm and was designed for the CPRM/CPPM digital rights management scheme which are used by DRM-restricted Secure Digital cards and DVD-Audio discs.- Cipher...
(also termed C2). The specification is kept secret and is accessible only to licensees. The scheme has not been broken or hacked, but this feature of SD cards is rarely actually used to protect content. DVD-Audio
DVD-Audio
DVD-Audio is a digital format for delivering high-fidelity audio content on a DVD. DVD-Audio is not intended to be a video delivery format and is not the same as video DVDs containing concert films or music videos....
uses the same DRM scheme.
Windows Phone 7
Windows Phone 7
Windows Phone is a mobile operating system developed by Microsoft, and is the successor to its Windows Mobile platform, although incompatible with it. Unlike its predecessor, it is primarily aimed at the consumer market rather than the enterprise market...
devices use SD cards designed to be accessed 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". Symbian devices, however, are some of the very few which 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
Nokia N8
The Nokia N8 is a Symbian^3 smartphone of the Nokia Nseries and Nokia's flagship device of 2010. It was released on 23 September 2010 at the Nokia Online Store before being released in markets around the world on 1 October 2010. The N8 features a 12 megapixel camera, a pentaband 3.5G radio and...
to reformat the card for subsequent use in other devices.
The Super Digital cards manufactured by Super*Talent are the same in appearance and function as Secure Digital cards, but they lack the CPRM feature of Secure Digital cards.
Power use
The power consumption of microSD cards varies by manufacturer, but appears to be in the range of 66-330 mW (20-100 mA at a supply voltage of 3.3 V). Specifications from TwinMos technologies list a maximum of 149 mW (45 mA) during transfer. Toshiba, on the other hand, lists 264-330 mW (80-100 mA).Speeds
An SD card's speed is measured by how quickly an amount of information can be read from, or written to, the card. 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 camcorderCamcorder
A camcorder is an electronic device that combines a video camera and a video recorder into one unit. Equipment manufacturers do not seem to have strict guidelines for the term usage...
built for a Class 6 card may suffer dropouts or corrupted video if a slower card is used. Digital camera
Digital camera
A digital camera is a camera that takes video or still photographs, or both, digitally by recording images via an electronic image sensor. It is the main device used in the field of digital photography...
s may experience a noticeable lag between shots, while the camera writes the picture to a slower card.
A card's speed depends on many factors, such as the following:
- The likelihood of soft errors that the card's controller must re-try
- The fact that, on most cards, writing data requires the controller to read and erase a larger region, then rewrite that entire region with the desired part changed
- The possibility of fragmentationFragmentation-In biology:* Fragmentation , a form of asexual reproduction* Fragmentation * Habitat fragmentation* Population fragmentation-Music:* Fragmented , the debut album from the Filipino independent band Up Dharma Down-Other:...
: that a body of information the host views as a unit is, for historical reasons, written to non-contiguous regions of memory. (This possibility does not cause rotational or head-movement delays as with magnetic media, but it does vary the amount of computation the card's controller must do.)
In early SD cards, the speed was measured with the × rating, which compared the average speed of reading data to that of the original CD-ROM
CD-ROM
A CD-ROM is a pre-pressed compact disc that contains data accessible to, but not writable by, a computer for data storage and music playback. The 1985 “Yellow Book” standard developed by Sony and Philips adapted the format to hold any form of binary data....
drive. Currently, the official unit of measurement is the Speed Class Rating, which guarantees a minimum rate at which data can be written to the card.
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.
Speed Class Rating
The Speed Class Rating is the official unit of speed measurement for SD cards. The class number guarantees a minimum write speed as a multiple of 8 Mbit/s (1 MB/s). The SD Association defines several speed class ratings, but manufacturers may claim conformance to those ratings without independent verification.Unlike the earlier "×" speed ratings, the host device can read a card's speed class. A device can warn the user if the card reports a speed class that falls below an application's minimum need.
These are the ratings of all currently available cards:
-
-
- {| class="wikitable"
-
|-
! Class !! Speed
|-
| Class 2 || 2 MB/s
|-
| Class 4 || 4 MB/s
|-
| Class 6 || 6 MB/s
|-
| Class 10 || 10 MB/s
|}
Speed Classes 2, 4, and 6 assert that the card supports the respective number of MB/s 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. By comparison, the older "×" rating measured maximum speed under ideal conditions, and was vague as to whether this was read speed or write speed.
Recent developments
On 21 May 2009, Panasonic
Panasonic
Panasonic is an international brand name for Japanese electric products manufacturer Panasonic Corporation, which was formerly known as Matsushita Electric Industrial Co., Ltd...
announced new class 10 SDHC cards, claiming that this new class is "part of SD Card Specification Ver.3.0". Toshiba also announced cards based on the new 3.0 spec.
On 1 June 2010, Pretec announced the new Class-16 HD-video grade SDXC 64 GB card at Computex Taipei 2010.
× rating
The × rating is a multiple of the standard CD-ROMCD-ROM
A CD-ROM is a pre-pressed compact disc that contains data accessible to, but not writable by, a computer for data storage and music playback. The 1985 “Yellow Book” standard developed by Sony and Philips adapted the format to hold any form of binary data....
drive speed of 1.2 Mbit/s (approximately 150 kB/s). Basic cards transfer data up to six times (6×) the CD-ROM speed; that is, 7.2 Mbit/s. The 2.0 specification 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. Vendors including Transcend and Kingston
Kingston Technology
Kingston Technology Company, Inc. is an American privately held, multinational computer technology corporation that develops, manufactures, sells and supports flash memory products and other computer-related memory products. Headquartered in Fountain Valley, California, USA, Kingston Technology...
report their cards' write speed.
This table lists common ratings, the minimum transfer rates, and the corresponding Speed Class (though the comparison is not always exact).
-
-
- {| class="wikitable"
-
|-
! valign="top" | Rating
! valign="top" | Read Speed
(Mbit/s)
! valign="top" | Read Speed
(MB/s)
! valign="top" | Write Speed
(Mbit/s)
! valign="top" | Write Speed
(MB/s)
! valign="top" | Speed
Class
|- style="text-align:right;"
|| 6×
|| 7.2
|| 0.9
||
||
||
|- style="text-align:right;"
|| 10×
|| 12.0
|| 1.5
||
||
||
|- style="text-align:right;"
|| 13×
|| 16.0
|| 2.0
|| 16.0
|| 2.0
|| 2
|- style="text-align:right;"
|| 26×
|| 33.0
|| 4.0
|| 32.0
|| 4.0
|| 4
|- style="text-align:right;"
|| 32×
|| 38.4
|| 4.8
|| 40.0
|| 5.0
||
|- style="text-align:right;"
|| 40×
|| 48.0
|| 6.0
|| 48.0
|| 6.0
|| 6
|- style="text-align:right;"
|| 66×
|| 80.0
|| 10.0
|| 80.0
|| 10.0
|| 10
|- style="text-align:right;"
|| 100×
|| 120.0
|| 15.0
|| 120.0
|| 15.0
||
|- style="text-align:right;"
|| 133×
|| 160.0
|| 20.0
|| 160.0
|| 20.0
||
|- style="text-align:right;"
|| 150×
|| 180.0
|| 22.5
|| 180.0
|| 22.5
||
|- style="text-align:right;"
|| 200×
|| 240.0
|| 30.0
|| 240.0
|| 30.0
||
|- style="text-align:right;"
|| 266×
|| 320.0
|| 40.0
|| 320.0
|| 40.0
||
|- style="text-align:right;"
|| 300×
|| 360.0
|| 45.0
|| 360.0
|| 45.0
||
|- style="text-align:right;"
|| 400×
|| 480.0
|| 60.0
|| 480.0
|| 60.0
||
|- style="text-align:right;"
|| 600×
|| 720.0
|| 90.0
|| 720.0
|| 90.0
||
|}
UHS Speed Class
The Ultra-High Speed (UHS) interface is available on some SDHC and SDXC cards. The card shows its support for UHS on its label, and reports to the host device that it supports UHS. Two ultra-high speeds are specified:- UHS-I provides a maximum data transfer rate is 104 MB/s, a quadrupling of the original top rate of 25 MB/s. This is the only class for which products are currently available.
- UHS-II further raises the data transfer rate to a theoretical maximum of 312 MB/s.
UHS memory cards work best with UHS host devices. The combination lets the user record HD resolution videos to tapeless camcorder
Tapeless Camcorder
A tapeless camcorder is a camcorder that does not use video tape for the digital recording of video productions as 20th century ones did. Tapeless camcorders record video as digital computer files onto random access data storage devices such as optical discs, hard disk drives and solid-state flash...
s while performing other functions. It is also suitable for real-time broadcasts and capturing large HD videos.
The maximum transfer rate of SDXCs that follow the SD 3.0 specification was announced to be 832 Mbit/s. (These are called UHS104 speeds.) The SD 4.0 specification is planned to increase this to 2.4 Gbit/s.
Use of UHS requires that the host device first take the following actions:
- Select the 4-bit transfer mode
- Command the card to drop from 3.3-volt to 1.8-volt operation.
Types of cards
The Secure Digital Card association extended the SD specification in various ways:- It defined electrically identical cards in smaller sizes: miniSD and microSD (originally named TransFlash). Smaller cards are usable in larger slots through use of a passive adapter. By comparison, Reduced Size MultiMediaCards (RS-MMCs)MultiMediaCardThe MultiMediaCard is a flash memory memory card standard. Unveiled in 1997 by Siemens AG and SanDisk, it is based on Toshiba's NAND-based flash memory, and is therefore much smaller than earlier systems based on Intel NOR-based memory such as CompactFlash. MMC is about the size of a postage...
are simply shorter MMCs and can be used in MMC slots by use of a physical extender. - It defined higher-capacity cards, some with faster speeds and added capabilities: SDHC (Secure Digital High Capacity) and SDXC (Secure Digital eXtended Capacity). These cards redefine the interface so that they cannot be used in older host devices.
- It defined an SDIO card family that provides input-output functions and may also provide memory functions. These cards are only fully functional in host devices designed to support their input-output functions.
Storage capacity and incompatibilities
All SD cards let the host device determine how much information the card can hold, and the specification of each SD family gives the host device a guarantee of the maximum capacity a compliant card will report.By the time the Version 2.0 (SDHC) specification was completed in June 2006, vendors had already devised 2 GB and 4 GB SD cards, either as specified in Version 1.1, or by creatively reading it, or by violating it but remaining in its framework. The resulting cards devices do not work correctly in some host devices.
SDSC cards above 1 GB
A host device can ask any inserted SD card for its 128-bit identification string (the Card-Specific Data or CSD). In standard-capacity cards (SDSC), 12 bits identify the number of memory clusters (ranging from 1 to 4,096) and 3 bits identify the number of blocks per cluster (which decode to 4, 8, 16, 32, 64, 128, 256, or 512 blocks per cluster). The host device multiplies these figures (as shown in the following section) with the number of bytes per block to determine the card's capacity in bytes.In SD version 1.00, the number of bytes per block was assumed to be 512. This permitted SDSC cards up to 4,096 × 512 × 512 = 1 GB, for which there are no known incompatibilities.
Version 1.01 let an SDSC card use a 4-bit field to indicate 1,024 or 2,048 bytes per block instead. Doing so enabled cards with 2 GB and 4 GB capacity.
Early SDSC host devices that assume 512-byte blocks therefore will not fully support the insertion of 2 GB or 4 GB cards. In some cases, the host device can read data that happens to reside in the first 1 GB of the card. If the assumption is made in the driver software, success may differ from one version of Windows to another. In addition, any host device might not support a 4 GB SDSC card, since the specification lets it assume that 2 GB is the maximum for these cards.
Storage capacity calculations
The format of the Card-Specific Data (CSD) register changed between version 1 (SDSC) and version 2.0 (which defines SDHC and SDXC).Version 1
In CSD Version 1, capacity is calculated as follows:
Capacity=(C_SIZE+1)<<(C_SIZE_MULT+2)<
9 || READ_BL_LEN
10The SD Card Association specification states: "To make 2 GByte card, the Maximum Block Length (READ_BL_LENWRITE_BL_LEN) shall be set to 1024 bytes. However, the Block Length, set by CMD16, shall be up to 512 bytes to keep consistency with 512 bytes Maximum Block Length cards (Less than and equal 2 Gbyte cards)."
Version 2.0
In Version 2.0, which defines SDHC and SDXC cards, the C_SIZE portion of the CSD is 32 bits and it indicates the memory size in multiples of 512 bytes. SDHC cards are allowed to use only 26 of the 32 bits, giving a maximum size of 32 GB. In addition, the C_SIZE_MULT field is removed and the READ_BL_LEN is no longer used to compute capacity. Two bits that were formerly reserved and fixed at 0 are now called the CSD Structure and identify the card family: 0 is SDSC; 1 is high (SDHC) and extended (SDXC) capacity; 2 and 3 are reserved. Older host devices are not aware of this new field and cannot correctly identify SDHC or SDXC cards.
Capacity is calculated thus:
Capacity=(C_SIZE+1)*524288
where for SDHC 4112<=C_SIZE<=65375 (approx. 2 GB) < capacity < 32 GiB
for SDXC 65535<=C_SIZE 32 GiB <= capacity <= 2 TiB max.
Capacities above 4 GB can only be achieved by following Version 2.0. In addition, capacities equal to 4 GB must also follow Version 2.0 to guarantee compatibility.
An SDHC card could be built to report a C_SIZE value above 65375, which would indicate a capacity of over 32 GB. This would violate the Version 2.0 specification, while complying with the format of the C_SIZE field. A host device that relied on C_SIZE rather than the guarantees in the specification to determine the card's capacity might support such a card. But the card might fail in other SDHC-compatible host devices.
Backward-compatibility
All SDHC readers are able to use standard SD cards, and all SDXC readers are able to use SD and SDHC cards.SDHC
SDHC (Secure Digital High Capacity) is defined in Version 2.0 of the SD specification. It supports cards with capacities up to 32 GB. The SDHC trademark is licensed to ensure compatibility.SDHC cards are physically and electrically identical to standard-capacity SD cards (SDSC). The major compatibility issues between SDHC and SDSC cards, as covered above, are the redefinition of the Card-Specific Data (CSD) register in Version 2.0, and the fact that SDHC cards are typically shipped preformatted with the FAT32 file system.
Host devices that accept SDHC cards are required to accept SDSC cards. However, host devices designed for SDSC do not recognize SDHC memory cards, although some devices can do so through a firmware upgrade. Microsoft Windows may need a hotfix to support accessing SDHC cards.
SDXC
The Secure Digital Extended Capacity (SDXC) format was unveiled at Consumer Electronics ShowConsumer Electronics Show
The International Consumer Electronics Show is a major technology-related trade show held each January in the Las Vegas Convention Center, Las Vegas, Nevada, United States. Not open to the public, the Consumer Electronics Association-sponsored show typically hosts previews of products and new...
(CES) 2009 (January 7–10, 2009). The maximum capacity defined for SDXC cards is 2 TB
Terabyte
The terabyte is a multiple of the unit byte for digital information. The prefix tera means 1012 in the International System of Units , and therefore 1 terabyte is , or 1 trillion bytes, or 1000 gigabytes. 1 terabyte in binary prefixes is 0.9095 tebibytes, or 931.32 gibibytes...
(2048 GB). The older SDHC cards also have a maximum capacity of 2 TB based on the card data structures, but this is artificially limited to 32 GB by the SD 2.0 specification. The first SDXCs being released are governed by an SD 3.0 specification (which also still specifies FAT32 and thus lower capacities), whereas higher capacity and faster SDXCs are expected to follow an SD 4.0 specification, which was formally announced in January 2011.
The SDcard association selected Microsoft
Microsoft
Microsoft Corporation is an American public multinational corporation headquartered in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions...
's proprietary exFAT
ExFAT
exFAT is a proprietary, patent-pending file system designed especially for USB flash drives. Developed by Microsoft, it is supported in Windows XP and Windows Server 2003 with update KB955704, Windows Embedded CE 6.0, Windows Vista with Service Pack 1, Windows Server 2008, Windows 7, Windows...
file system in the official SDXC specification; however, as with SD and SDHC, it is still a plain block device
Block (data storage)
In computing , a block is a sequence of bytes or bits, having a nominal length . Data thus structured are said to be blocked. The process of putting data into blocks is called blocking. Blocking is used to facilitate the handling of the data-stream by the computer program receiving the data...
and thus arbitrary partitioning and other file systems can be used, such as btrFS
Btrfs
Btrfs is a GPL-licensed copy-on-write file system for Linux.Development began at Oracle Corporation in 2007....
, ext4
Ext4
The ext4 or fourth extended filesystem is a journaling file system for Linux, developed as the successor to ext3.It was born as a series of backward compatible extensions to ext3, many of them originally developed by Cluster File Systems for the Lustre file system between 2003 and 2006, meant to...
, HFS Plus
HFS Plus
HFS Plus or HFS+ is a file system developed by Apple Inc. to replace their Hierarchical File System as the primary file system used in Macintosh computers . It is also one of the formats used by the iPod digital music player...
, NTFS
NTFS
NTFS is the standard file system of Windows NT, including its later versions Windows 2000, Windows XP, Windows Server 2003, Windows Server 2008, Windows Vista, and Windows 7....
, UFS
Unix File System
The Unix file system is a file system used by many Unix and Unix-like operating systems. It is also called the Berkeley Fast File System, the BSD Fast File System or FFS...
, etc.
History
On January 7, 2009, SanDiskSanDisk
SanDisk Corporation is an American multinational corporation that designs, develops and manufactures data storage solutions in a range of form factors using the flash memory, controller and firmware technologies. It was founded in 1988 by Dr. Eli Harari and Sanjay Mehrotra, non-volatile memory...
and Sony
Sony
, commonly referred to as Sony, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan and the world's fifth largest media conglomerate measured by revenues....
announced the joint development of the XC variant of the competing Memory Stick
Memory Stick
Memory Stick is a removable flash memory card format, launched by Sony in October 1998, and is also used in general to describe the whole family of Memory Sticks...
format, boasting the same 2 TB maximum capacity of SDXC.
On January 8, 2009, Panasonic
Panasonic
Panasonic is an international brand name for Japanese electric products manufacturer Panasonic Corporation, which was formerly known as Matsushita Electric Industrial Co., Ltd...
announced plans for production of 64 GB SDXC cards.
On March 6, 2009, Pretec introduced the world's first SDXC card with a capacity of 32 GB and a read/write speed of 400 Mbit/s. At the introduction, there were no products compatible with the new memory card.
On August 3, 2009, Toshiba
Toshiba
is a multinational electronics and electrical equipment corporation headquartered in Tokyo, Japan. It is a diversified manufacturer and marketer of electrical products, spanning information & communications equipment and systems, Internet-based solutions and services, electronic components and...
announced it will launch the world's first 64 GB SDXC Memory Card with a read speed of 480 Mbit
Megabit
The megabit is a multiple of the unit bit for digital information or computer storage. The prefix mega is defined in the International System of Units as a multiplier of 106 , and therefore...
/s. The 64 GB card (THNSU064GAA2BC) was planned to be available in the spring of 2010. Toshiba card was available from April 13.
On January 6, 2010, Panasonic
Panasonic
Panasonic is an international brand name for Japanese electric products manufacturer Panasonic Corporation, which was formerly known as Matsushita Electric Industrial Co., Ltd...
announced its first SDXC cards with 64 GB and 48 GB to be available in February (RP-SDW64GE1K and RP-SDW48GE1K).
On January 6, 2010, Sony
Sony
, commonly referred to as Sony, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan and the world's fifth largest media conglomerate measured by revenues....
announced the launch of Handycam HDR-CX55V with SDXC support.
On February 8, 2010, Canon announced the launch of the new EOS Rebel T2i
Canon EOS 550D
The Canon EOS 550D is an 18.0 megapixel digital single-lens reflex camera, announced by Canon on February 8, 2010. It was made available starting February 24, 2010 and to US dealers starting early March. It is known as the EOS Kiss X4 in Japan, and as the EOS Rebel T2i in North America...
Digital SLR camera, the first EOS model to support SDXC memory cards.
On February 19, 2010, Panasonic
Panasonic
Panasonic is an international brand name for Japanese electric products manufacturer Panasonic Corporation, which was formerly known as Matsushita Electric Industrial Co., Ltd...
launched in Japan World's first available for consumers SDXC memory cards with 64 GB and 48 GB (RP-SDW64GE1K and RP-SDW48GE1K) together with USB card readers compatible with SDXC format.
On February 22, 2010, SanDisk
SanDisk
SanDisk Corporation is an American multinational corporation that designs, develops and manufactures data storage solutions in a range of form factors using the flash memory, controller and firmware technologies. It was founded in 1988 by Dr. Eli Harari and Sanjay Mehrotra, non-volatile memory...
launched its 64 GB SanDisk Ultra SDXC card.
The first integrated SDXC card readers are available from JMicron and are expected to be used in laptops in 2010.
In January, 2011, Centon Electronics, Inc.
Centon Electronics, Inc.
Centon Electronic, Inc. is an American privately held, multinational computer technology corporation that develops, manufactures, sells and supports flash memory products and other computer-related memory products. Headquartered in Aliso Viejo, California, USA...
began shipping its 64 GB and 128 GB Class 10 SDXC card.
In March, 2011, Lexar
Lexar
Lexar Media, Inc. is an American manufacturer of digital media products based in Fremont, CA. Products manufactured by Lexar include SD cards, Memory Sticks, keydrives, CompactFlash cards and card readers. Lexar's Memory Stick Duos also have versions adapted for the PSP which includes a version of...
began shipping its 128 GB Class 10 SDXC card.
In September 2011, a 64 GB microSDXC card was released by SanDisk
SDHC and SDXC compatibility issues
In the 3.0 specification, the electronic interface of SDHC and SDXC cards is the same. This means that SDHC hosts that have drivers that recognize the newly used capability bits, and have operating system software that understands the exFATExFAT
exFAT is a proprietary, patent-pending file system designed especially for USB flash drives. Developed by Microsoft, it is supported in Windows XP and Windows Server 2003 with update KB955704, Windows Embedded CE 6.0, Windows Vista with Service Pack 1, Windows Server 2008, Windows 7, Windows...
filesystem, are compatible with SDXC cards. The decision to label cards with a capacity greater than 32 GB as SDXC and to use a different filesystem is due solely to the limitations in creating larger filesystems in certain versions of Microsoft Windows. Other operating system kernels, such as Linux, make no distinction between SDHC and SDXC cards, as long as the card contains a compatible filesystem.
SDHC and SDXC cards and hosts have these compatibility issues:
- Existing SDHC hosts will only support the SDXC cards at up to UHS104 speeds.
- SDXC hosts are backward compatible with SD and SDHC memory cards.
- The operating systems that support SDXC, as of 2011, are: Linux (with a proprietary driver for the exFAT filesystem), Microsoft Windows 7, Windows Vista SP1+, Windows XP SP2 or SP3 with KB955704, Windows Server 2008 SP1+, Windows Server 2003 SP2 or SP3 with KB955704, Windows CE 6+, Mac OS X 10.6.5 or later.
SDIO
A SDIO (Secure Digital Input Output) card is an extension of the SD specification to cover I/O functions. Host devices that support SDIO (typically PDAs like the Palm Treo, but occasionally laptops or mobile phones) can use the SD slot to support GPS receivers, modemModem
A modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data...
s, barcode reader
Barcode reader
A barcode reader is an electronic device for reading printed barcodes. Like a flatbed scanner, it consists of a light source, a lens and a light sensor translating optical impulses into electrical ones...
s, FM radio tuners, TV tuners, RFID readers, digital camera
Digital camera
A digital camera is a camera that takes video or still photographs, or both, digitally by recording images via an electronic image sensor. It is the main device used in the field of digital photography...
s, and interfaces to Wi-Fi
Wi-Fi
Wi-Fi or Wifi, is a mechanism for wirelessly connecting electronic devices. A device enabled with Wi-Fi, such as a personal computer, video game console, smartphone, or digital audio player, can connect to the Internet via a wireless network access point. An access point has a range of about 20...
, Bluetooth
Bluetooth
Bluetooth is a proprietary open wireless technology standard for exchanging data over short distances from fixed and mobile devices, creating personal area networks with high levels of security...
, Ethernet
Ethernet
Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....
, and IrDA
Infrared Data Association
The Infrared Data Association defines physical specifications communications protocol standards for the short-range exchange of data over infrared light, for uses such as personal area networks ....
. 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 8 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.
Host support for SDIO
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. (Bluetooth devices exhibit comparable compatibility issues, although to a lesser extent thanks to standardized Bluetooth profiles.)
Vendor enhancements
Vendors have sought to differentiate their products in the market through various vendor-specific features:- Integrated Wi-FiWi-FiWi-Fi or Wifi, is a mechanism for wirelessly connecting electronic devices. A device enabled with Wi-Fi, such as a personal computer, video game console, smartphone, or digital audio player, can connect to the Internet via a wireless network access point. An access point has a range of about 20...
— Eye-FiEye-FiEye-Fi is a company based in Mountain View, California that produces SD memory cards and SDHC cards with Wi-Fi capabilities. Using an Eye-Fi card inside a camera, one can wirelessly and automatically upload digital photos to a local computer...
produces several SD cards with built-in Wi-Fi transceivers providing 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. Some models geotagWi-Fi Positioning SystemWi-Fi-based positioning system emerged as an idea that can solve the positioning in certain situations , taking advantage of the rapid growth of wireless access points in urban areas...
their pictures. - Pre-loaded content — In 2006, SanDisk announced GruviGruviGruvi was a short-lived memory card format compatible with microSD developed by Sandisk in 2006. The cards were intended for the distribution of music and videos, and had a variety of special Digital rights management features including the ability to pre-load content that could be 'unlocked' at a...
, a microSD card with extra Digital Rights Management (DRM) features, with which to use memory cards as a medium to sell content. SanDisk again announced pre-loaded cards in 2008, under the slotMusicSlotMusicslotMusic is a type of microSD memory card developed by SanDisk preloaded with music in MP3 format. They were first available at Wal-Mart and Best Buy stores in the United States in October 2008. The current selection of songs comes from Universal Music Group, Sony BMG, Warner Music Group and EMI...
name, this time not using any of the DRM capabilities of the SD card. In 2011, SanDisk offered various collections of 1000 songs on a single slotMusic card for about $40, now restricted to compatible devices and without the ability to copy the files. - Integrated USB connector — The SanDiskSanDiskSanDisk Corporation is an American multinational corporation that designs, develops and manufactures data storage solutions in a range of form factors using the flash memory, controller and firmware technologies. It was founded in 1988 by Dr. Eli Harari and Sanjay Mehrotra, non-volatile memory...
SD Plus product can be plugged directly into a USB port without needing a USB card reader. 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 an SD card with a digital display that would show how much free space was left on the card.
Market penetration
Secure Digital cards are ubiquitous in consumer electronic devices, and have become the dominant means of storing several gigabytes of data in a small size.Devices such as netbooks, digital camera
Digital camera
A digital camera is a camera that takes video or still photographs, or both, digitally by recording images via an electronic image sensor. It is the main device used in the field of digital photography...
s, camcorder
Camcorder
A camcorder is an electronic device that combines a video camera and a video recorder into one unit. Equipment manufacturers do not seem to have strict guidelines for the term usage...
s, personal digital assistant
Personal digital assistant
A personal digital assistant , also known as a palmtop computer, or personal data assistant, is a mobile device that functions as a personal information manager. Current PDAs often have the ability to connect to the Internet...
(PDAs), mobile phone
Mobile phone
A mobile phone is a device which can make and receive telephone calls over a radio link whilst moving around a wide geographic area. It does so by connecting to a cellular network provided by a mobile network operator...
s, video game console
Video game console
A video game console is an interactive entertainment computer or customized computer system that produces a video display signal which can be used with a display device to display a video game...
s, digital audio players, and many others use them.
Smaller devices tend to use microSD or miniSD rather than full sized SD cards.
SD cards are not generally used in mass produced devices where only a small amount of storage is needed due to economic reasons, or where a very large amount of storage is needed.
Digital cameras
Toshiba
is a multinational electronics and electrical equipment corporation headquartered in Tokyo, Japan. It is a diversified manufacturer and marketer of electrical products, spanning information & communications equipment and systems, Internet-based solutions and services, electronic components and...
's SmartMedia
SmartMedia
SmartMedia is a flash memory card standard owned by Toshiba, with capacities ranging from 2 MB to 128 MB. SmartMedia memory cards are no longer manufactured.- History :...
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, with cards not being easily available in 2007.
At this time all the leading digital camera manufacturers use SD in their consumer product lines, including Canon
Canon Inc.
is a Japanese multinational corporation that specialises in the manufacture of imaging and optical products, including cameras, camcorders, photocopiers, steppers and computer printers. Its headquarters are located in Ōta, Tokyo, Japan.-Origins:...
, Casio
Casio
is a multinational electronic devices manufacturing company founded in 1946, with its headquarters in Shibuya, Tokyo, Japan. Casio is best known for its electronic products, such as calculators, audio equipment, PDAs, cameras, musical instruments, and watches...
, Fujifilm
Fujifilm
is a multinational photography and imaging company headquartered in Tokyo, Japan.Fujifilm's principal activities are the development, production, sale and servicing of color photographic film, digital cameras, photofinishing equipment, color paper, photofinishing chemicals, medical imaging...
, Kodak, Leica, Nikon
Nikon
, also known as just Nikon, is a multinational corporation headquartered in Tokyo, Japan, specializing in optics and imaging. Its products include cameras, binoculars, microscopes, measurement instruments, and the steppers used in the photolithography steps of semiconductor fabrication, of which...
, Olympus
Olympus Corporation
is a Japan-based manufacturer of optics and reprography products. Olympus was established on 12 October 1919, initially specializing in microscope and thermometer businesses. Its global headquarters are in Shinjuku, Tokyo, Japan, while its USA operations are based in Center Valley, Pennsylvania,...
, Panasonic
Panasonic
Panasonic is an international brand name for Japanese electric products manufacturer Panasonic Corporation, which was formerly known as Matsushita Electric Industrial Co., Ltd...
, Pentax
Pentax
Pentax is a brand name used by Hoya Corporation for its medical-related products & services and Pentax Ricoh Imaging Company for cameras, sport optics , etc. Hoya purchased and merged with the Japanese optics company on March 31, 2008. Hoya's Pentax imaging business was sold to Ricoh Company, Ltd...
, Ricoh
Ricoh
or Ricoh, is a Japanese company that was established in 1936 on February 6th, as , a company in the RIKEN zaibatsu. Its headquarters is located in Ricoh Building in Chūō, Tokyo....
, Samsung
Samsung
The Samsung Group is a South Korean multinational conglomerate corporation headquartered in Samsung Town, Seoul, South Korea...
, and Sony
Sony
, commonly referred to as Sony, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan and the world's fifth largest media conglomerate measured by revenues....
. Formerly, Olympus
Olympus Corporation
is a Japan-based manufacturer of optics and reprography products. Olympus was established on 12 October 1919, initially specializing in microscope and thermometer businesses. Its global headquarters are in Shinjuku, Tokyo, Japan, while its USA operations are based in Center Valley, Pennsylvania,...
and Fujifilm
Fujifilm
is a multinational photography and imaging company headquartered in Tokyo, Japan.Fujifilm's principal activities are the development, production, sale and servicing of color photographic film, digital cameras, photofinishing equipment, color paper, photofinishing chemicals, medical imaging...
used XD-Picture Card
XD-Picture Card
xD-Picture Card is a flash memory card format, used mainly in older digital cameras. xD stands for Extreme Digital.xD cards are available in capacities of 16 MiB up to 2 GiB.- History :...
s (xD cards) exclusively, while Sony
Sony
, commonly referred to as Sony, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan and the world's fifth largest media conglomerate measured by revenues....
only used Memory Stick
Memory Stick
Memory Stick is a removable flash memory card format, launched by Sony in October 1998, and is also used in general to describe the whole family of Memory Sticks...
; however , all three support SD.
Some prosumer
Prosumer
Prosumer is a portmanteau formed by contracting either the word professional or less often, producer with the word consumer. For example, a prosumer grade digital camera is a "cross" between consumer grade and professional grade...
and professional digital camera
Digital camera
A digital camera is a camera that takes video or still photographs, or both, digitally by recording images via an electronic image sensor. It is the main device used in the field of digital photography...
models continue to offer CompactFlash
CompactFlash
CompactFlash is a mass storage device format used in portable electronic devices. Most CompactFlash devices contain flash memory in a standardized enclosure. The format was first specified and produced by SanDisk in 1994...
, either on a second card slot or as the only storage, as it has historically offered a better price/capacity ratio and faster transfer rates.
Secure Digital memory cards can be used in Sony XDCAM
XDCAM
XDCAM is a a series of products for digital recording using random access solid-state memory media, introduced by Sony in 2003. Four different product lines — the XDCAM SD, XDCAM HD, XDCAM EX and XDCAM HD422 — differ in types of encoder used, frame size, container type and in...
EX camcorder
Camcorder
A camcorder is an electronic device that combines a video camera and a video recorder into one unit. Equipment manufacturers do not seem to have strict guidelines for the term usage...
s via the MEAD-SD01 adapter.
Personal computers
Although many personal computerPersonal computer
A personal computer is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end-user with no intervening computer operator...
s accommodate SD cards as an auxiliary storage device through a built-in slot or a USB adaptor, SD cards cannot be used as the primary hard disk
Hard disk
A hard disk drive is a non-volatile, random access digital magnetic data storage device. It features rotating rigid platters on a motor-driven spindle within a protective enclosure. Data is magnetically read from and written to the platter by read/write heads that float on a film of air above the...
because none of the SD card variants supports ATA signaling. This use requires a separate SD controller chip or a SD-to-CompactFlash converter.
Embedded systems
In 2008, the SD Card Association specified Embedded SD, "leverag[ing] well-known SD standards" to enable non-removable SD-style devices on printed circuit boards. SanDisk provides such memory components under the iNAND brand.Most modern microcontroller
Microcontroller
A microcontroller is a small computer on a single integrated circuit containing a processor core, memory, and programmable input/output peripherals. Program memory in the form of NOR flash or OTP ROM is also often included on chip, as well as a typically small amount of RAM...
s have built-in SPI
Serial Peripheral Interface Bus
The Serial Peripheral Interface Bus or SPI bus is a synchronous serial data link standard named by Motorola that operates in full duplex mode. Devices communicate in master/slave mode where the master device initiates the data frame. Multiple slave devices are allowed with individual slave select ...
logic that can interface to a 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 Linksys
Linksys
Linksys by Cisco, commonly known as Linksys, is a brand of home and small office networking products now produced by Cisco Systems, though once a separate company founded in 1995 before being acquired by Cisco in 2003...
WRT54G
WRT54G
The Linksys WRT54G is a Wi-Fi capable residential gateway from Linksys. The device is capable of sharing Internet connections among several computers via 802.3 Ethernet and 802.11b/g wireless data links.-WRT54G:The original WRT54G was first released in December 2002...
router with MMC support code from the Linux kernel
Linux kernel
The Linux kernel is an operating system kernel used by the Linux family of Unix-like operating systems. It is one of the most prominent examples of free and open source software....
. This technique can achieve throughput of up to .
Openness of standards
Like most memory card formats, SD is covered by numerous patentPatent
A patent is a form of intellectual property. It consists of a set of exclusive rights granted by a sovereign state to an inventor or their assignee for a limited period of time in exchange for the public disclosure of an invention....
s and trademark
Trademark
A trademark, trade mark, or trade-mark is a distinctive sign or indicator used by an individual, business organization, or other legal entity to identify that the products or services to consumers with which the trademark appears originate from a unique source, and to distinguish its products or...
s. Three versions of the SD specification have been set: 1.0, 1.1 and 2.0. These were originally available only after agreeing to a non-disclosure agreement
Non-disclosure agreement
A non-disclosure agreement , also known as a confidentiality agreement , confidential disclosure agreement , proprietary information agreement , or secrecy agreement, is a legal contract between at least two parties that outlines confidential material, knowledge, or information that the parties...
(NDA) that prohibited development of an open source
Open source
The term open source describes practices in production and development that promote access to the end product's source materials. Some consider open source a philosophy, others consider it a pragmatic methodology...
driver, which generated consternation in the open-source and free software
Free software
Free software, software libre or libre software is software that can be used, studied, and modified without restriction, and which can be copied and redistributed in modified or unmodified form either without restriction, or with restrictions that only ensure that further recipients can also do...
communities. However, the system was eventually reverse-engineered, and the non-DRMed sections of the memory cards could be accessed by free software drivers. Since then, the SD Card Association
SD Card Association
The SD Card Association develops and publishes technical standards for SD Card technology, and promotes the use of the technology. SD Cards are compact data storage devices used to store digital files, such as picture files recorded by digital cameras. The association was founded on 28 January...
(SDA) has made access to a simplified version of the specification available under a less restrictive license. Although most open-source drivers were written before this, it has helped them to solve some compatibility issues.
In 2006, the SD Card Association also released a simplified version of their host controller interface specification (not to be confused with the physical specification, which covers the actual cards and their protocol) and later also for physical layer, ASSD extensions, SDIO
SDIO
SDIO may refer to:* Secure Digital Input Output, a type of Secure Digital card interface.* Strategic Defense Initiative Organization, an organization set up to oversee the Strategic Defense Initiative; now known as the Missile Defense Agency....
and SDIO
SDIO
SDIO may refer to:* Secure Digital Input Output, a type of Secure Digital card interface.* Strategic Defense Initiative Organization, an organization set up to oversee the Strategic Defense Initiative; now known as the Missile Defense Agency....
Bluetooth
Bluetooth
Bluetooth is a proprietary open wireless technology standard for exchanging data over short distances from fixed and mobile devices, creating personal area networks with high levels of security...
Type-A specifications under a disclaimers agreement. Like the physical specification, most of the information had already been discovered before the public release and at least Linux
Linux
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
had a fully free driver for it. Still, building a chip conforming to this specification caused the One Laptop per Child project to claim "the first truly Open Source SD implementation, with no need to obtain an SDI license or sign NDAs to create SD drivers or applications."
For the most part, the lack of a complete, open SD specification mainly affects embedded system
Embedded system
An embedded system is a computer system designed for specific control functions within a larger system. often with real-time computing constraints. It is embedded as part of a complete device often including hardware and mechanical parts. By contrast, a general-purpose computer, such as a personal...
s and laptop systems, since desktop users generally read SD cards via USB-based card readers. These card readers present a standard USB mass storage interface to memory cards, thus separating the operating system from the details of the underlying SD interface. However, embedded systems (such as portable music players) usually access SD cards directly, and therefore complete programming information is necessary. Desktop card readers are themselves examples of such embedded systems; the manufacturers of these readers have usually paid the SDCA for complete access to the SD specifications. Many notebook computers now include SD card readers not based on USB; device drivers for these essentially access the SD card directly, as in embedded systems.
Royalties for SD card licences are imposed for manufacture and sale of memory cards and host adapters (USD$1,000/year plus membership at USD$1,500/year) but SDIO cards can be made without royalties and MMC host adapters do not require a royalty. MMCs have a seven-pin interface; SD and SDIO have expanded this to nine pins and MMC Plus expands this even further with thirteen pins.
Compared to other flash memory formats
Overall, SD is less open than CompactFlashCompactFlash
CompactFlash is a mass storage device format used in portable electronic devices. Most CompactFlash devices contain flash memory in a standardized enclosure. The format was first specified and produced by SanDisk in 1994...
or USB flash memory drives
USB flash drive
A flash drive is a data storage device that consists of flash memory with an integrated Universal Serial Bus interface. flash drives are typically removable and rewritable, and physically much smaller than a floppy disk. Most weigh less than 30 g...
; these are open standard
Open standard
An open standard is a standard that is publicly available and has various rights to use associated with it, and may also have various properties of how it was designed . There is no single definition and interpretations vary with usage....
s which can be implemented free of payment for licensing, royalties, or documentation. (CompactFlash and USB flash drives may, however, require licensing fees for the use of associated logo
Logo
A logo is a graphic mark or emblem commonly used by commercial enterprises, organizations and even individuals to aid and promote instant public recognition...
s and trademark
Trademark
A trademark, trade mark, or trade-mark is a distinctive sign or indicator used by an individual, business organization, or other legal entity to identify that the products or services to consumers with which the trademark appears originate from a unique source, and to distinguish its products or...
s.)
However, SD is much more open than Memory Stick
Memory Stick
Memory Stick is a removable flash memory card format, launched by Sony in October 1998, and is also used in general to describe the whole family of Memory Sticks...
, for which no public documentation nor any documented legacy implementation is available. All SD cards can be accessed freely using the well-documented SPI
Serial Peripheral Interface Bus
The Serial Peripheral Interface Bus or SPI bus is a synchronous serial data link standard named by Motorola that operates in full duplex mode. Devices communicate in master/slave mode where the master device initiates the data frame. Multiple slave devices are allowed with individual slave select ...
bus.
xD
XD-Picture Card
xD-Picture Card is a flash memory card format, used mainly in older digital cameras. xD stands for Extreme Digital.xD cards are available in capacities of 16 MiB up to 2 GiB.- History :...
cards are simply 18-pin NAND flash chips in a special package and support the standard command set for raw NAND flash access. Although the raw hardware interface to xD cards is well understood, the layout of its memory contents—necessary for interoperability with xD card readers and digital cameras—is totally undocumented. The consortium that licenses xD cards has not released any technical information to the public.
See also
- SD Card AssociationSD Card AssociationThe SD Card Association develops and publishes technical standards for SD Card technology, and promotes the use of the technology. SD Cards are compact data storage devices used to store digital files, such as picture files recorded by digital cameras. The association was founded on 28 January...
- Comparison of memory cardsComparison of memory cardsThis table provides summary of comparison of various flash memory cards, .- Common information :-Physical details:Note that a memory card's dimensions are determined while holding the card with contact pins upwards. The length of cards is often greater than their width...
- Serial Peripheral Interface BusSerial Peripheral Interface BusThe Serial Peripheral Interface Bus or SPI bus is a synchronous serial data link standard named by Motorola that operates in full duplex mode. Devices communicate in master/slave mode where the master device initiates the data frame. Multiple slave devices are allowed with individual slave select ...
(SPI) - File Allocation TableFile Allocation TableFile Allocation Table is a computer file system architecture now widely used on many computer systems and most memory cards, such as those used with digital cameras. FAT file systems are commonly found on floppy disks, flash memory cards, digital cameras, and many other portable devices because of...
(FAT16, FAT32) and exFATExFATexFAT is a proprietary, patent-pending file system designed especially for USB flash drives. Developed by Microsoft, it is supported in Windows XP and Windows Server 2003 with update KB955704, Windows Embedded CE 6.0, Windows Vista with Service Pack 1, Windows Server 2008, Windows 7, Windows... - Flash memoryFlash memoryFlash memory is a non-volatile computer storage chip that can be electrically erased and reprogrammed. It was developed from EEPROM and must be erased in fairly large blocks before these can be rewritten with new data...
- slotMusicSlotMusicslotMusic is a type of microSD memory card developed by SanDisk preloaded with music in MP3 format. They were first available at Wal-Mart and Best Buy stores in the United States in October 2008. The current selection of songs comes from Universal Music Group, Sony BMG, Warner Music Group and EMI...
- MultiMediaCardMultiMediaCardThe MultiMediaCard is a flash memory memory card standard. Unveiled in 1997 by Siemens AG and SanDisk, it is based on Toshiba's NAND-based flash memory, and is therefore much smaller than earlier systems based on Intel NOR-based memory such as CompactFlash. MMC is about the size of a postage...
- USB FlashCardUSB FlashCardUSB FlashCard is a flash memory card format developed by Lexar, and announced on December 13, 2004.There is a wide range of existing memory card formats such as SD, xD, and CompactFlash; the major advantage of USB FlashCard is that the cards are in fact standard USB flash drives...
- Universal Flash StorageUniversal Flash StorageUniversal Flash Storage is a proposed common flash storage specification for digital cameras, mobile phones and consumer electronic devices...
External links
Organizations, SD Association, sdcard.org-
- Membership: $2000/yr for General, $4500/yr for Executive.
- Full Specification: Free for members, $1000/yr for R&D non-members.
Specifications
- SD Simplified Specifications, sdcard.org, Free
- Part 1, Physical Layer, v3.01
- Part A1, ASSD Extension, v2.00
- Part A2, SD Host Controller, v3.00
- Part E1, SDIO, v3.00
- Part E2, SDIO Bluetooth Type-A, v1.00
- Microsoft Extensible Firmware Initiative FAT32 File System Specification, Microsoft
Software
Comparisons
- Comparison of numerous memory cards and readers, plus technical information, hjreggel.net
- SDHC Card comparison (german), hardware-infos.com
- Speed Testing of UHS-1 Cards in prosumer Nikon D7000 Camera
- Nikon D7000 Memory speed tests, SDHC Memory Cards: including Sandisk Extreme Pro UHS Speed Class 1 45 Mbyte/s and Several Popular Class 10 SDHC Cards
Interfacing
- Interfacing to SD cards, great technical details
- Interfacing AVR (Arduino) to SD cards, C source code
- Interfacing ARM to SD cards, C source code
- Interfacing MSP430 to SD cards, C source code, Michigan State University
- Interfacing MAXQ2000 to SD cards, good technical descriptions, C source code, maxim-ic.com
- SD card controller, Verilog source code, opencores.org