MultiMediaCard
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The MultiMediaCard (MMC) 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 stamp: 24 mm x 32 mm x 1.4 mm. MMC originally used a 1-bit serial interface, but newer versions of the specification allow transfers of 4 or sometimes even 8 bits at a time. They have been more or less superseded by Secure Digital cards (SD card), but still see significant use because MMC cards can be used in most devices which support SD cards and they are cheaper than SD cards.
Typically, an MMC card is used as storage media for a portable device, in a form that can easily be removed for access by a PC. For example, a digital camera would use an MMC card for storing image files. With an MMC reader (typically a small box that connects via USB or some other serial connection, although some can be found integrated into the computer itself), a user could copy the pictures taken with the digital camera off to his or her computer. Modern computers, both laptops and desktops, often have SD slots, which can additionally read MMC cards if the operating system drivers support them.
MMC cards are currently available in sizes up to and including 4 GB with 8 GB models announced but not yet available. They are used in almost every context in which memory cards are used, like cellular phones, digital audio players, digital cameras and PDAs. Since the introduction of Secure Digital card and SDIO (Secure Digital Input/Output) slot few companies build MMC slots into their devices, but the slightly thinner, pin-compatible MMC cards can be used in almost any device that supports SD cards if the software/firmware on the devices support them. An exception is some mobile devices like the Nokia 9300 communicator, where the smaller size of the MMC card is a benefit.
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[edit] Open standard
This technology is a standard available to any company who wants to develop products based on it. However, the specification is not available for free - it must be bought from the MMC Association[1] who impose considerable restrictions on how the specification can be used[2].
Having said this, Samsung (a major backer of MMC) provides a highly detailed datasheet[3] which contains much of the essential information for writing an MMC driver.
[edit] Reduced-Size MultiMediaCard (RS-MMC)
MMC cards also come in a smaller form factor, of about half the size: 24 mm × 18 mm × 1.5 mm. This alternate form factor is known as Reduced-Size MultiMediaCard, or RS-MMC, and was introduced in 2004. RS-MMC cards are simply smaller MMC cards; by using a simple mechanical adapter to elongate the card, an RS-MMC card can be used in any MMC (or SD) slot. RS-MMC cards are currently available in sizes up to and including 2 GB with 4 GB models announced but unavailable.
The only significant hardware licensors of RS-MMC cards were Nokia and Siemens, who used to use RS-MMC in their Series 60 Symbian smartphones, the Nokia 770 Internet Tablet (Nokia), and generations 65 and 75 (Siemens). However, since 2006 all of Nokia's new smartphone and card-compatible normal phone models have used miniSD or microSD cards, with the company appearing to abandon the MMC standard in its products. Siemens exited the mobile phone business completely in 2006.
[edit] Dual-Voltage MultimediaCard (DV-MMC)
One of the first substantial changes in MMC was the introduction of dual-voltage cards that support operations at 1.8 V in addition to 3.3 V. Running at lower voltages reduces the card's power consumption, which is important in mobile devices. However, simple dual-voltage parts quickly went out of production in favour of MMCplus and MMCmobile which offer additional capabilities on top of dual-voltage support.
[edit] MMCplus and MMCmobile
The version 4.x of the MMC standard, introduced in 2005, brought in two very significant changes to compete against SD cards. These were support for running at higher speeds (26MHz, 52MHz) than the original MMC (20MHz) or SD (25MHz, 50MHz) and 4 or 8 bit wide data buses.
Version 4.x full-size cards and reduced-size cards can be marketed as MMCplus and MMCmobile respectively.
Version 4.x cards are fully backward compatible with existing readers but require updated hardware/software to use their new capabilities; even though the 4 bit wide bus and high-speed modes of operation are deliberately electrically compatible with SD, the initialization protocol is different, so firmware/software updates are required to allow these features to be enabled when the card is used in an SD reader.
[edit] MMCmicro
MMCmicro is a micro-size version of MMC. With dimensions of 14 mm × 12 mm × 1.1 mm, it is even smaller and thinner than RS-MMC. Like MMCmobile, MMCmicro supports dual voltage, is backward compatible with MMC, and can be used in full-size MMC and SD slots with a mechanical adapter. MMMmicro cards support the high-speed and 4 bit bus features of the 4.x spec, but not the 8 bit bus, due to the absence of the extra pins[4]
MMCmicro cards appears very similar to microSD but the two formats are not physically compatible and have irreconcilable pinouts.
[edit] SecureMMC
An additional, optional, part of the MMC 4.x specification is a DRM mechanism intended to enable MMC to compete with SD or Memory Stick in this area. Very little information is known about how SecureMMC works or how its DRM characteristics compare with its competitors.
[edit] See also
[edit] External links
- MultiMediaCard Association
- Sandisk OEM Manual for MMC and RS-MMC (PDF)
- KingMax MMC technical document (PDF)
- MMC Wiki
- MMC pinout (tech.)
- MMCplus pinout (tech.)
[edit] References
- ^ MMCA: Specification for Non-Members, www.mmca.org, 2007
- ^ Product Information and License Agreement, www.mmca.org, 2007
- ^ Samsung MMC Datasheet, http://www.samsung.com 2007
- ^ Samsung's MMCmicro description, http://www.samsung.com 2007
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