Secure Digital (
SD) is a
non-volatile memory card format
developed by Matsushita, SanDisk, and
Toshiba for use in portable devices.
Today it is widely used in digital
cameras, handheld computers, PDAs, Media
Players, mobile phones, GPS receivers,
and video game consoles. Standard SD
card capacities range from 4 MB to 4 GB,
and for high capacity SDHC cards from 4
GB to 32 GB as of 2008. The SDXC (eXtended
Capacity), a new specification announced
at the 2009 CES, will allow for 2 TB
capacity cards.
The format has proven
to be very popular. A change in the
format, however, while allowing
capacities greater than 4 GB (SDHC), has
created compatibility issues with older
devices that cannot read the new format.
The fact that SDHC format cards have the
same physical shape and form factor as
the older format has caused considerable
confusion for consumers.[1][2]
SDHC cards require SDHC-capable device
firmware generally not found with older
devices.
History
In August 1999, Panasonic, SanDisk,
and Toshiba first agreed to develop and
market the SD (Secure Digital) Memory
Card, which was a development of the MMC.
With a physical profile of 24 mm × 32 mm
× 2.1 mm, the new card provided both DRM
up to the 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 previous year,
featured MagicGate DRM, and was
physically larger. It was mistakenly
predicted that DRM features [2] would be
widely used due to pressure from music
and other media suppliers to prevent
piracy.
At the 2000 CES trade show
Matsushita, SanDisk and Toshiba
Corporation announced the creation of
the SD Card Association to promote SD
cards. It is headquartered 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
megabytes available 3 months later.
In April 2006, the SDA released a
detailed specification for the
non-security related parts of the SD
Memory Card standard. The organization
also released specifications for the
SDIO (Secure Digital Input Output) cards
and the standard SD host controller.
During the same year, specifications
were finalized for the small form-factor
microSD (formerly known as TransFlash)
and SDHC, with capacities in excess of
2 GB and a minimum sustained read/write
speed of 2.2 MB/s.
|
Source. |
An SD card, mini SD card, and micro SD card from top to bottom.
|
Design and
implementation
SD cards are based on the older
MultiMediaCard (MMC) format, but have a
number of differences:
- The SD card is asymmetrically
shaped in order not to be inserted
upside down, while an MMC would go
in most of the way but not make
contact if inverted.
- Most SD cards are physically
thicker than MMCs. SD cards
generally measure 32 mm × 24 mm ×
2.1 mm, but as with MMCs can be as
thin as 1.4 mm.
- 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 10-20 MB/s,
but this number is subject to
change, due to recent improvements
to the MMC standard.[3]
Devices with SD slots can use
the thinner MMCs, but standard SD cards
will not fit into the thinner 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 readers 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.
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 notched corner).
On the left side may be a
write-protection notch. If this is
present, the card cannot be written to.
If the notch is covered by a sliding
write protection tab, or absent, then
the card is writeable. This can be
overridden if the device reading it
wishes to (and supports it).
Not all devices support write
protection, which is an optional feature
of the SD standard.
Some SD cards have no
write-protection notch,[4]
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 capabilities.
Such media are usually permanently
marked read-only by adding the notch
with no tab.
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File
system
Like other flash card technologies,
most SD cards ship preformatted with the
FAT or FAT 32 file system. The ubiquity
of this file system allows the card to
be accessed on virtually any host device
with an SD reader. Also, standard FAT
maintenance utilities (e.g. ScanDisk)
can be used to repair or retrieve
corrupted data. However, because the
card appears as a removable hard drive
to the host system, the card can be
reformatted to any file system supported
by the operating system.
SD cards of size 4 GB and lower can
be formatted to either FAT16 (4 GB card
can be formatted to FAT16 only with 64k
clusters) or FAT32 file systems. Cards 8
GB and larger can only be formatted with
a file system that can handle these
larger storage sizes, such as FAT32.
Defragmentation tools are used on
hard disks to optimize the file system
access speed. On an SD card, this is
pointless, as any block can be accessed
as fast as any other. Doing this will
wear the card out slightly, as a limited
number of writes can be made before
failure.
Speeds
There are different speed grades
available which are measured with the
same system as CD-ROMs, in multiples of
150 kB/s (1x = 150 kB/s). Basic cards
transfer data up to six times (6x) the
data rate of the standard CD-ROM speed
(900 kB/s vs. 150 kB/s). High-speed
cards are made with higher data transfer
rates like 66x (10 MB/s), and high-end
cards have speeds of 200x or higher.
Note that maximum read speed and
maximum write speed may be
different, with maximum write speed
typically lower than maximum read speed.
Some digital cameras require high-speed
cards (write speed) to record video
smoothly or capture multiple still
photographs in rapid succession. Higher
speeds of up to 200x are defined by
specification 2.0.
The following table lists some common
ratings and their respective minimum
transfer rates.
| Rating |
Speed (MB/s) |
SDHC Class |
| 6x |
0.9 |
n/a |
| 13x |
2.0 |
2 |
| 26x |
4.0 |
4 |
| 32x |
4.8 |
4 |
| 40x |
6.0 |
6 |
| 66x |
10.0 |
6 |
| 100x |
15.0 |
6 |
| 133x |
20.0 |
6 |
| 150x |
22.5 |
6 |
| 200x |
30.0 |
6 |
| 266x |
40.0 |
6 |
| 300x |
45.0 |
6 |
Openness
of standards
Like most memory card formats, SD is
covered by numerous patents (e.g. US
patent 5602987) and trademarks.
There are three versions of the SD
specification: 1.0, 1.1 and 2.0. These
were originally available only after
agreeing to a non-disclosure agreement
(NDA) which prohibits the development of
an open source driver, a fact that
generates a fair amount of consternation
in the open-source and free software
communities. The system was eventually
reverse-engineered though, and the non-DRMed
sections of the memory cards could be
accessed by free software drivers.
These days however, the SD Card
Association (SDA) has made access to a
simplified version of the specification
available under a less-restrictive
licence.[5]
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).[6]
Like the physical specification, most of
the information had already been
discovered before the public release[7]
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."[8]
For the most part, the lack of
complete, open SD specifications mainly
affects embedded 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.
Technical
explanation
SD supports at least three transfer
modes:
- One-bit SD mode: separate
command and data channels and a
proprietary transfer format.
- Four-bit SD mode: uses
extra pins plus some reassigned
pins.
- SPI mode: Serial
Peripheral Interface Bus, a simpler
subset of the SD protocol for use
with microcontrollers.
All memory cards must support all
three modes, except for microSD where
SPI is optional. The cards must also
support clock frequencies of up to
25 MHz for regular cards, and 50 MHz for
high-speed cards.
Royalties for SD/SDIO licenses are
imposed for manufacture and sale of
memory cards and host adapters (1000 USD
per year plus membership at 1500
USD/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.
DRM
features
The digital rights management scheme
embedded in the SD cards is defined as
the Content Protection for Recordable
Media (CPRM) by the 4C Entity and is
centered around use of the Cryptomeria
cipher (also known as C2). The
specification is kept secret and is
accessible only to licensees. DVD-Audio
uses a very similar scheme known as
Content Protection for Prerecorded Media
(CPPM). This DRM has not been seen "in
the wild" and few, if any, devices
appear to provide support for it.
Super*Talent, a manufacturer of
computer memory, has created the "Super
Digital" card. They are the same in
appearance and function to regular
Secure Digital cards, but they lack the
CPRM code commonly found in Secure
Digital cards.
[9]
Compared
to other flash memory formats
Overall, SD is less open than
CompactFlash or USB flash memory drives,
which can be implemented free of charge,
but require licensing fees for the
associated logos and trademarks.
However, SD is much more open than
Memory Stick, for which no public
documentation nor any documented legacy
implementation is available. All SD
cards (other than microSD) can, at
least, be accessed freely using the
well-documented SPI/MMC mode.
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 publicly available
technical information.
Different
types of MMC/SD cards
The SD card is not the only flash
memory card standard ratified by the
Secure Digital Card Association. Other
SD Card Association formats include
miniSD, microSD (formerly known as
TransFlash before ratification by the SD
Card Association), and SDHC (Secure
Digital High Capacity, for capacities
above 4 GB – although, there are cards
some readers cannot handle over 1 GB
that are not SDHC). SDHC is not fully
compatible with the format that it
extends, in that SD devices that do not
specifically support SDHC will not work
with the newer cards.
These smaller miniSD and microSD
cards are usable in full size MMC/SD/SDIO
slots with an adapter (which must route
the electrical connections as well as
making physical contact). It should be
noted, however, that it is already
difficult to create I/O devices in the
SD form factor and this will be even
more difficult in the smaller sizes.
However, a WiFi card for mini-SDIO is
already available from Spectec.[10]
As SD slots still support MMCs, the
separately-evolved smaller MMC variants
are also compatible with SD-supporting
devices. Unlike miniSD and microSD
(which are sufficiently different from
SD to make mechanical adapters
necessary), RS-MMC slots maintain
backward compatibility with full-sized
MMCs, because the RS-MMCs are simply
shorter MMCs. More information on these
variants can be found in the article
about the MultiMediaCard standard.
It is also important to note, that
unlike for data storage (which typically
works everywhere an SD slot is present),
an SDIO device must be supported and
equipped with drivers and applications
for the host system and usually does not
work outside of the manufacturer's scope
(which means, for example, that an HP
SDIO camera usually does not work with
PDAs for which it is not listed as an
accessory). This behavior is often not
expected by end users who typically
expect that only the SD slot is
required. Similar compatibility are
sometimes seen with Bluetooth devices,
although to a much lesser extent thanks
to standardized bluetooth profiles.
Most, possibly all, current MMC flash
memory cards support SPI mode even if
not officially required as failure to do
so would severely affect compatibility.
All cards currently made by SanDisk,
Ritek/Ridata, and Kingmax digital appear
to support SPI. Also, MMCs may be
electrically identical to SD cards but
in a thinner package and with an
electronic fuse blown to disable SD
functionality (so no SD royalties need
to be paid). Some MicroSD cards do not
support SPI mode.
MMC defined the SPI and one-bit MMC/SD
protocols. The underlying SPI protocol
has existed for years as a standard
feature on many microcontrollers. From a
societal perspective, the justification
for a new incompatible SD/MMC protocol
is questionable; the development of a
new incompatible and unnecessary
protocol may help trade associations
collect licensing and membership fees
but it raises the cost of hardware and
software in many ways. The new protocol
used open collector signaling to allow
multiple cards on the same bus but this
actually causes problems at higher clock
rates. While SPI used three shared lines
plus a separate chip select to each
card, the new protocol allows up to 30
cards to be connected to the same three
wires (with no chip select) at the
expense of a much more complicated card
initialization and the requirement that
each card have a unique serial number
for plug and play operation; this
feature is rarely used and its use is
actively discouraged in new standards
(which recommend a completely separate
channel to each card) because of speed
and power consumption issues. The
quasi-proprietary one-bit protocol was
extended to support four bit wide (SD
and MMC) and eight bit (MMC only)
transfers for more speed while much of
the rest of the computer industry is
moving to higher speed narrower
channels; standard SPI could simply have
been clocked at higher data rates (such
as 133 MHz) for higher performance than
offered by four-bit SD — embedded CPUs
that did not already have higher clock
rates available would not have been fast
enough to handle the higher data rates
anyway. The SD card association dropped
support for some of the old one-bit MMC
protocol commands and added support for
additional commands related to copy
protection.
Compatibility issues with 2 GB and
larger cards
Devices that use SD cards identify
the card by requesting a 128-bit
identification string from the card. For
standard-capacity SD cards, 12 of the
bits are used to identify the number of
memory clusters (ranging from 1 to 4096)
and 3 of the bits are used to identify
the number of blocks per cluster (which
decode to 4, 8, 16, 32, 64, 128, 256 or
512 blocks per cluster).
In older 1.x implementations the
standard capacity block was exactly 512
bytes. This gives 4096 x 512 x 512 = 1
gigabyte of storage memory. A later
revision of the 1.x standard allowed a
4-bit field to indicate 1024 or 2048
bytes per block instead, yielding more
than 1 gigabyte of memory storage.
Devices designed before this change may
incorrectly identify such cards, usually
by misidentifying a card with lower
capacity than is the case by assuming
512 bytes per block rather than 1024 or
2048.
For the new SDHC high capacity card
(2.0) implementation, 22 bits of the
identification string are used to
indicate the memory size in increments
of 512 KBytes. Currently 16 of the 22
bits are allowed to be used, giving a
maximum size of 32 GB. All SDHC 4-GB and
larger cards must be 2.0
implementations. Two bits that were
previously reserved and fixed at 0 are
now used for identifying the type of
card, 0=standard, 1=HC, 2=reserved,
3=reserved. Non-HC devices are not
programmed to read this code and
therefore cannot correctly read the
identification of the card.
All SDHC readers work with standard
SD cards.[11]
Many older devices will not accept
the 2 or 4 GB size even though it is in
the revised standard. The following
statement is from the SD association
specification:
- "To make 2 GByte card, the
Maximum Block Length (READ_BL_LEN=WRITE_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)."[12]
SD
(non-SDHC) cards with greater than 1 GB
capacity
The SD Card Association's current
specifications define how a standard SD
(non-SDHC) card with more than 1 GB and
up to 4 GB capacity should be designed.
These cards should be readable in any SD
1.01 devices that take the block length
data into account. Any 1 GB or lesser
card should always work. (So the key
question is how one's reader handles
block length).
According to the specification,[13]
the maximum capacity of a standard SD
card is defined by (BLOCKNR x BLOCK_LEN),
where BLOCKNR may be (4096 x 512) and
BLOCK_LEN may be up to 2048. This allows
a capacity of 4 GB. The main problem is
that some of the card readers support
only a block (aka. sector) size of 512
bytes, so greater than 1 GB non-SDHC
cards may cause compatibility
difficulties for some users.
SDHC cards
with greater than 32 GB capacity
Similarly to the above, as of version
2.00 of the specification,[13]
the capacity of an SDHC card is limited
to 32 GB. However, while not strictly
adhering to that standard, it is in
principle possible to create SDHC-like
cards of up to 2048 GB capacity. SDHC
cards have fixed sector size of 512
bytes.
SDHC
SDHC (Secure Digital High Capacity,
SD 2.0) is an extension of the SD
standard that appeared in June 2006.[14]
SDHC allows standard-compliant
capacities in excess of 4 GB. SDHC cards
are often formatted with the FAT32 file
system.[15]
It uses the same physical and electrical
form factor as SD, but the SD 2.0
standard in SDHC uses a different memory
addressing method (sector addressing vs
byte addressing), thus theoretically
reaching a maximum capacity of up to 2
TB (2048 GB). Currently the SD Card
association has artificially defined the
maximum limit of SDHC capacity to 32 GB[16],
however the SD card specification states
that "SD Memory Cards with a capacity
greater than 32 GB will be available
with updated versions of [the
specification]."[17]
SDHC cards work only in SDHC compatible
devices, but standard SD cards work in
both SD and SDHC devices. The SDHC
trademark is licensed to ensure
compatibility.[18]
SD Speed
Class Ratings
SDHC cards have SD Speed Class
Ratings defined by the SD Association.
The SD Speed Class Ratings specify the
following minimum write speeds based on
"the best fragmented state where no
memory unit is occupied":[19]
- Class 2: 2 MB/s - 13x
- Class 4: 4 MB/s - 26x
- Class 6: 6 MB/s - 40x
SDHC cards will often also advertise
a maximum speed (such as 133x or 150x)
in addition to this minimum Speed Class
Rating. See section speeds above for a
further explanation. One critical
difference between the Speed Class and
the maximum speed ratings is the ability
of the host device to query the SD card
for the speed class and determine the
best location to store data that meets
the performance required. "Maximum
speed" ratings are quoted by the
manufacturers but unverified by any
independent evaluation process.
SD and
SDHC compatibility issues
During early 2007, the simultaneous
availability of 4 GB SD cards compliant
with later revisions of version 1.x of
the SD specification but incompatible
with readers based on earlier revisions
of the specification, and of 4 GB SDHC
cards, and incompatibilities between SD
and SDHC caused confusion among
consumers buying memory devices. Several
Manufacturers such as Sandisk, Alcotek,
Toshiba and Hynix have developed SDHC
cards that are now fully compatible with
the SDHC SD2.0 specification.
SD and SDHC cards and devices have
these compatibility issues :
- Devices that do not specifically
support SDHC do not recognize SDHC
memory cards. Nonetheless, some
devices require only a firmware
upgrade.[20]
- SDHC devices are backward
compatible with SD memory cards.[20]
- Some manufacturers have produced
4 GB SD cards that conform to
neither the SD2.0/SDHC spec nor
existing SD devices.[21]
- File System: SD cards are
typically formatted with the FAT16
file system, while SDHC cards are
typically formatted as FAT32.[18]
However, both types of cards can
support other general-purpose file
systems, such as UFS2/ext2 or the
proprietary exFAT for example.
SDXC
The Secure Digital Extended Capacity
(SDXC) format was unveiled at CES 2009.
The maximum capacity defined for SDXC
cards is 2 TB (2048 GB). SDHC cards also
have a maximum capacity of 2 TB based on
the card data structures, but this is
arbitrarily limited to 32 GB by the SD
2.0 document.
The maximum transfer rate of SDXC was
announced as 104 MB/s, with plans to
increase it to 300 MB/s in the future.
The SDXC specification has selected
Microsoft's proprietary exFAT file
system as the standard for this memory
card format;[22][23][24]
however, as with SDHC and SD, it is
possible to use another filesystem such
as FAT32 or ext2.
On January 8, 2009, Panasonic
announced plans for production of 64 GB
SDXC cards.[25]
On March, 6, 2009, Pretec introduces
world's first SDXC card
[26] with a capacity of 32 GB and
a read/write speed of 50 MB/s. At the
introduction there were no products
compatible with the new memory card.
SDIO
SDIO stands for Secure Digital Input
Output.
An SDIO card is an combination of an
SD card and an I/O device. This kind of
combination is increasingly found in
portable electronics devices.
Devices that support SDIO
(typically PDAs like the Palm Treo, but
occasionally laptops or mobile phones)
can use small devices designed for the
SD form factor, like GPS receivers,
Wi-Fi or Bluetooth adapters, modems,
Ethernet adapters, barcode readers, IrDA
adapters, FM radio tuners, TV tuners,
RFID readers, digital cameras, or other
mass storage media such as hard drives.
A number of other devices have been
proposed but not yet implemented,
including RS-232 serial adapters,
fingerprint scanners, SDIO to USB
host/slave adapters (which would allow
an SDIO-equipped handheld device to use
USB peripherals and/or interface to
PCs), magnetic strip readers,
combination Bluetooth/Wi-Fi/GPS
transceivers, cellular modems (PCS, CDPD,
GSM, etc.), and APRS/TNC adapters.
SDIO cards are fully compatible with
SD Memory Card host controller
(including mechanical, electrical,
power, signaling and software). When an
SDIO card is inserted into a non SDIO-aware
host, it will cause no physical damage
or disruption to device or host
controller. SPI bus topology is
mandatory for SDIO, unlike SD Memory.
Most of the SD Memory commands are not
supported in SDIO. SDIO cards can
contain 8 separate logical cards, though
at the moment this is at most a memory
and IO function. SD slots will take SD
cards only. SDIO slots will take SD
cards and SDIO cards.
SD cards
with extra features
Various manufacturers have tried to
make their SD cards stand out from the
crowd in different ways
- SD Plus - A type of SD
card made by Sandisk that has an
integrated USB connector so it can
be plugged directly into a USB port
without needing any special card
reader.[27]
This concept has proven successful
and other companies started
introducing similar designs branded
as duo SD.
- Capacity Display - In
2006 A-DATA announced an SD card
with its own digital display that
would show how much free space is
left on the card.
[28]
- Eye-Fi, Inc. - Produces
an SD card with Wi-Fi capability
built in for 802.11g, 802.11b and
backwards-compatible 802.11n
wireless networks and supporting
static WEP 40/104/128, WPA-PSK,
WPA2-PSK security standards. The
card works with any digital camera
with an SD slot and can transmit
captured images over a wireless
network. When not in range of a
wireless network connection, the
card makes use of its 2 GB capacity
(EYE-FI-2 GB model) until the images
can be transferred.[29]
- MyMemory produces an SD
card (SDIO) with Wi-Fi capability
built in for 802.11b and 802.11g
wireless networks, without storage
capacity for Windows Mobile and
Windows CE devices.
- Gruvi - A rare type of
microSD card with extra DRM features
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
cameras / camcorders, PDAs, mobile
phones and digital audio players as well
as 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 required.
Digital
cameras
SD/MMC cards have 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.
As of December 2008, nearly all
leading digital camera manufacturers use
SD in their product lines, including
Casio, Canon, Nikon, Pentax, Kodak,
Panasonic, Konica Minolta, Ricoh and
Samsung.
Some prosumer and professional camera
models continue to offer CompactFlash on
a second card slot, as it has
historically offered a better
price/capacity ratio and faster transfer
rates.
Two major manufacturers, however,
have stuck to their own proprietary card
formats: Olympus uses xD cards, and Sony
uses Memory Stick. Prior to 2007,
Fujifilm also used xD cards exclusively,
but has added SD functionality to all
models released since then, while
Olympus has released an xD-microSD
adapter for their latest cameras. Even
Olympus have added microSD
functionality. They equipped their newer
cameras with a microSD adapter.
Embedded
systems
Neither SD card variant supports ATA,
limiting their use as solid state disks
unless a separate converter chip is
used. Although embedded systems exist
that use SD cards as their main storage
mechanism, a special SD controller chip
is often used.[30]
In September 2008, the SD Card
Association announced the Embedded SD
standard to be released in November.[31]
A homebrew hardware hack has brought
SD card support to the popular WRT54G
router by utilising spare GPIO pins on
the router's processor and the Linux
kernel's MMC module. Transfer speeds of
200KiB/s can be achieved with this
setup.[32]
