| 词条 | MultiMediaCard |
| 释义 |
| name = MultiMediaCard | logo = | image = 15-04-29-MMC-Karte-RalfR-dscf4734-d.jpg | caption = 32 MB MMCplus card | type = Memory card | encoding = | capacity = Up to 512 GB | read = | write = | standard = | owner = JEDEC | use = Portable devices | dimensions = Standard: 32 × 24 × 1.4 mm | weight = Standard: ~2.0 g | extended from = | extended to = Secure Digital (SD) }} MultiMediaCard, officially abbreviated as MMC, is a memory card standard used for solid-state storage. Unveiled in 1997 by SanDisk and Siemens AG,[1] MMC is based on a surface-contact low pin-count serial interface using a single memory stack substrate assembly, and is therefore much smaller than earlier systems based on high pin-count parallel interfaces using traditional surface-mount assembly such as CompactFlash. Both products were initially introduced using SanDisk NOR-based flash technology. MMC is about the size of a postage stamp: 24 mm × 32 mm × 1.4 mm. MMC originally used a 1-bit serial interface, but newer versions{{when?|date=March 2018}} of the specification allow transfers of 4 or 8 bits at a time. MMC can be used in many devices that can use Secure Digital (SD) cards. Typically, an MMC operates as a storage medium 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 for storing image files. Via 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 transfer pictures taken with the digital camera to his or her computer. Modern computers, both laptops and desktops, often have SD slots, which can additionally read MMCs if the operating system drivers can. MMCs are available in sizes up to and including 512 GB. 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 SD cards, few companies build MMC slots into their devices (an exception is some mobile devices like the Nokia 9300 communicator in 2004, where the smaller size of the MMC is a benefit), but the slightly thinner, pin-compatible MMCs can be used in almost any device that can use SD cards if the software/firmware on the device is capable. While few companies build MMC slots into devices {{as of | 2018 | lc = on}} (SD cards are more common), the embedded MMC (eMMC) is still widely used in consumer electronics as a primary means of integrated storage in portable devices. It provides a low-cost flash-memory system with a built-in controller that can reside inside an Android or Windows phone or in a low-cost PC and can appear to its host as a bootable device, in lieu of a more expensive form of solid-state storage, such as a traditional solid-state drive. Open standardThis technology is a standard available to any company wanting to develop products based on it. There is no royalty charged for devices which host an MMC. A membership with the MMC Association must be purchased in order to manufacture the cards themselves. As of July 2009, the specifications version 4.4 (dated March 2009) can be requested from the MMCA, and after registering with MMCA, can be downloaded free of charge. Older versions of the standard, as well as some optional enhancements to the standard such as MiCard and SecureMMC, must be purchased separately. A highly detailed version is available on-line[2] that contains essential information for writing an MMC driver. As of 23 September 2008, the MMCA group has [https://web.archive.org/web/20080302013503/http://www.mmca.org/compliance/buy_spec/mmc_spec_v4_3/ turned over] all specifications to the JEDEC organization including embedded MMC (e-MMC) and miCARD assets. JEDEC is an organization devoted to standards for the solid-state industry. As of February 2015, the latest specifications version 5.1 can be requested from JEDEC, and after registering with JEDEC, can be downloaded free-of-charge. Older versions of the standard, as well as some optional enhancements to the standard such as MiCard and SecureMMC, must be purchased separately. VariantsRS-MMCIn 2004, the Reduced-Size MultiMediaCard (RS-MMC) was introduced as a smaller form factor of the MMC, about half the size: 24 mm × 18 mm × 1.4 mm. The RS-MMC uses a simple mechanical adapter to elongate the card so it can be used in any MMC (or SD) slot. RS-MMCs are currently available in sizes up to and including 2 GB. The modern continuation of an RS-MMC is commonly known as MiniDrive (MD-MMC). A MiniDrive is generally a microSD card adapter in the RS-MMC form factor. This allows a user to take advantage of the wider range of modern MMCs available[3] to exceed the historic 2 GB limitations of older chip technology. Implementations of RS-MMCs include Nokia and Siemens, who used RS-MMC in their Series 60 Symbian smartphones, the Nokia 770 Internet Tablet, and generations 65 and 75 (Siemens). However, since 2006 all of Nokia's new devices with card slots have used miniSD or microSD cards, with the company dropping support for the MMC standard in its products. Siemens exited the mobile phone business completely in 2006. Siemens continue to use MMC for some PLC storage leveraging MD-MMC advances. DV-MMCThe Dual-Voltage MultimediaCard (DV-MMC) is one of the first acceptable changes in MMC was the introduction of dual-voltage cards that can operate at 1.8 V in addition to 3.3 V. Running at lower voltages reduces the card's energy 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 capabilities in addition to dual-voltage capability. MMCplus and MMCmobileThe version 4.x of the MMC standard, introduced in 2005, brought in two very significant changes to compete against SD cards: ability to run at higher speeds (26 MHz and 52 MHz) than the original MMC (20 MHz) or SD (25 MHz, 50 MHz) and a four- or eight-bit-wide data bus. 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 four-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 use these features in an SD reader. MMCmicroMMCmicro 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 allows dual voltage, is backward compatible with MMC, and can be used in full-size MMC and SD slots with a mechanical adapter. MMCmicro cards have the high-speed and four-bit-bus features of the 4.x spec but not the eight-bit bus, due to the absence of the extra pins.[4]It was formerly known as S-card when introduced by Samsung on 13 December 2004. It was later adapted and introduced in 2005 by the MultiMediaCard Association (MMCA) as the third form factor memory card in the MultiMediaCard family.[5] MMCmicro appears very similar to microSD but the two formats are not physically compatible and have incompatible pinouts. MiCardThe MiCard is a backward-compatible extension of the MMC standard with a theoretical maximum size of 2048 GB (2 TB) announced on 2 June 2007. The card is composed of two detachable parts, much like a microSD card with an SD adapter. The small memory card fits directly in a USB port while it also has MMC-compatible electrical contacts, which with an included electromechanical adapter fits in traditional MMC and SD card readers. To date, only one manufacturer (Pretec) has produced cards in this format.[6] Developed by Industrial Technology Research Institute of Taiwan, at the time of the announcement twelve Taiwanese companies (including ADATA Technology, Asustek, BenQ, Carry Computer Eng. Co., C-One Technology, DBTel, Power Digital Card Co., and RiCHIP) had signed on to manufacture the new memory card. However, as of June 2011 none of the listed companies had released any such cards, and nor had any further announcements been made about plans for the format. The card was announced to be available starting in the third quarter of 2007. It was expected to save the 12 Taiwanese companies who planned to manufacture the product and related hardware up to US$40 million in licensing fees, that presumably would otherwise be paid to owners of competing flash memory formats. The initial card was to have a capacity of 8 GB, while the standard would allow sizes up to 2048 GB. It was stated to have data transfer speeds of 480 Mbit/s (60 Mbyte/s), with plans to increase data throughput over time. SecureMMCAn 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{{Citation needed|date=December 2008}} about how SecureMMC works or how its DRM characteristics compare with its competitors. eMMCThe eMMC (embedded MMC[7]) architecture puts the MMC components (flash memory plus controller) into a small ball grid array (BGA) IC package for use in circuit boards as an embedded non-volatile memory system. eMMC exists in 100, 153, 169 ball packages and is based on an 8-bit parallel interface.[8] This is noticeably different from other versions of MMC as this is not a user-removable card, but rather a permanent attachment to the circuit board. In the event of an issue stemming from either the memory or its controller, the PCB (printed circuit board) would need to be replaced or repaired. Almost all mobile phones and tablets used this form of flash for main storage up to 2016, when UFS started to take control of the market. The latest version of the eMMC standard (JESD84-B51) by JEDEC is version 5.1 released February 2015, with speeds rivaling discrete SATA-based SSDs (400 MB/s).[9] eMMC does not support the SPI-bus protocol. OthersIn 2004, Seagate, Hitachi and others introduced an interface called CE-ATA for small form factor hard disk drives.[10] This interface was electrically and physically compatible with the MMC specification. However, support for further development of the standard ended in 2008.[11] Table{{main|Comparison of memory cards}}{{Comparison of memory cards}}References1. ^{{cite book|url =http://www.tomshardware.com/reviews/flash-removable-storage-ssd-drive,3626-3.html | website= TomsHardware.com | title= Upgrading And Repairing PCs 21st Edition | publisher= Que Publishing | author= Scott Mueller | isbn= 978-0789750006 }} 2. ^{{cite web |url=http://html.alldatasheet.com/html-pdf/141187/SAMSUNG/MC2GH512NMCA-2SA00/305/1/MC2GH512NMCA-2SA00.html |title=MC2GH512NMCA-2SA00 datasheet(1/102 Pages) SAMSUNG | SAMSUNG MultiMediaCard |website=Html.AllDatasheet.com |date=2005-09-22 |accessdate=2013-11-13}} 3. ^TheMiniDrive.com, http://www.TheMiniDrive.com. Extracted 23 April 2014. 4. ^{{cite web|url=http://www.samsung.com/Products/Semiconductor/FlashCard/MMC/micro_mmc.htm |title=Samsung Semiconductor Global Official Website |language=ru |publisher=Samsung.com |date= |accessdate=2013-11-13}} 5. ^allmemorycards.com, MMCmicro. Extracted 22 April 2006. 6. ^{{cite web| title = Pretec Announces S-Diamond, 1st In the World to Implement miCARD Standard| url = http://www.businesswire.com/portal/site/google/index.jsp?ndmViewId=news_view&newsId=20070604006489&newsLang=en| accessdate = 21 January 2010 }} 7. ^{{cite web|url=http://www.datalight.com/solutions/technologies/emmc/what-is-emmc|title=What is eMMC Memory – software support - Reliance Nitro|author=|date=|website=datalight.com}} 8. ^https://www.hyperstone.com Flash Memory Form Factors - The Fundamentals of Reliable Flash Storage, Retrieved 19. April 2018 9. ^{{cite web|url=http://www.jedec.org/standards-documents/technology-focus-areas/flash-memory-ssds-ufs-emmc/e-mmc |title=e.MMC v5.1 |publisher=JEDEC |date= |accessdate=2015-08-21}} 10. ^{{cite web |title=New Consumer Electronic Interface On Future Hard Drives |url=https://phys.org/news/2004-09-consumer-electronic-interface-future-hard.html |website=Phys.org |accessdate=1 April 2019}} 11. ^{{cite web |title=Consumer Electronics ATA (CE-ATA) |url=https://www.techopedia.com/definition/26017/consumer-electronics-ata-ce-ata |website=Technopedia |accessdate=1 April 2019}} External links{{Commons category|Multi Media Card}}Organizations
Specifications
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4 : Open standards|SanDisk|Siemens|Computer-related introductions in 1997 |
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