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.SDHC cards require SDHC-capable device firmware generally not found with older devices.
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.SDHC cards require SDHC-capable device firmware generally not found with older devices.
History
Inside a 64 MB Panasonic SD Card with Samsung chip
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
Inside a 64 MB Panasonic SD Card with Samsung chip
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
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
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
Design and implementation
An SD card, mini SD card, and micro SD card from top to bottom.
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.
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
An SD card, mini SD card, and micro SD card from top to bottom.
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.
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
[edit] 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,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.[citation needed] Such media are usually permanently marked read-only by adding the notch with no 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,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.[citation needed] Such media are usually permanently marked read-only by adding the notch with no tab.
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