Numberous kinds of memory cards
2008-08-01

                                                                       Numberous Kinds Of Memory Card

A memory card (sometimes called a flash memory card or a storage card) is a small storage medium used to store data such as text, pictures, audio, and video, for use on small, portable or remote computing devices. There are several memory cards on the market, including the CF card (Compact Flash card), the Smart Media card, the MultiMedia Card (MMC), the Memory Stick, the SD card (secure digital card), the XD card and the USB(universal serial bus). These cards are of varying sizes, and each is available in a range of storage capacities that typically corresponds directly to the price. 1. CF(compact flash) In 1994, the CF card was first specified and produced by SanDisk, and after launched, it was widely used in many devices. But, in recent years it has been widely substituted by smaller SD cards on the consumer end, however it is still a preferred format for D-SLR cameras, for its superior capacity and reliability. In totally, the CF card has managed to be the most successful of the early memory card formats, outliving both Miniature Card, SmartMedia, and PC Card Type I in mainstream popularity. Now, there are two main subdivisions of CF cards, Type I and the thicker Type II (CF2) cards, and The CF Type II slot is used by Microdrives and some other devices. The only difference between the two types is thickness. The Type II devices are 5 mm thick while Type I devices are 3.3 mm thick. As of 2008, the CF cards are generally available in capacities from about 512 MB (512 MiB) to about 64 GB (64 GiB), with perhaps the most popular choices in Europe and North America being between 512 MB and 8 GB. Lower capacity cards, below 512 MB, are becoming rare in stores as higher capacity cards are readily available at the same price.

2. SM(smart media) The SM card was launched to compete with the Mini Card, Compact Flash, and PC card formats in the summer of 1995. The SM card, only 0.76mm thick, was one of the smallest and thinnest of the early memory cards, and managed to maintain a favorable cost ratio as compared to the others. But, the Smart Media cards lack a built-in controller chip, which kept the cost down. This feature later caused problems, since some older devices would require firmware updates to handle larger capacity cards. And, lacking of built-in controller also made it impossible for the card to perform automatic wear levelling, a process which prevents premature wearout of a sector by mapping the writes to various other sectors in the card. In the formats, the Smart Media cards come two, 5 V and the more modern 3.3 V (sometimes marked 3 V), named for their main supply voltages. Many older Smart Media devices only support 5V Smart Media cards, whereas many newer devices only support 3.3V cards. Now, the SM card which is larger than 128 MB was never released, although there were rumors of a 256 MB card being planned. Technical specifications for the memory size were released, and the 256 MB cards were even announced in some places.

3. MMC(multimedia card) 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-base memory such as Compact Flash. The MMC comes in a smaller form factor, of about half the size: 24 mm × 18 mm × 1.4 mm. This alternate form factor is known as Reduced-Size MultiMediaCard, or RS-MMC, and was introduced in 2004 , The only significant hardware licensors of RS-MMCs were Nokia and Siemens, who used to use 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 appearing to abandon the MMC standard in its products. Siemens exited the mobile phone business completely in 2006. Currently, the MMC is 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 so on. Modern computers, both laptops and desktops, often have SD slots, which can additionally read MMC if the operating system drivers support them.

4. Memory Stick Memory Stick is launched by SONY in October 1998, and is also used in general to describe the whole family of Memory Sticks. Now, the whole family of Memory Sticks includes four members, Memory Stick PRO, a revision that allows greater maximum storage capacity and faster file transfer speeds; Memory Stick DUO (including Memory Stick PRO DUO), a small-form-factor version of the Memory Stick; Memory Stick PRO-HG, a high speed variant of the PRO, to be used for high definition still and video cameras and Memory Stick MICRO (M2) which is even smaller. The original memory stick was available in sizes up to 128 MB, and a sub-version, Memory Stick Select allowed two banks of 128 MB selectable by a slider switch, essentially two cards squeezed into one. The largest capacity Memory Stick currently available is 16 GB which was unveiled at the 2008 Consumer Electronics Show in Las Vegas. According to Sony, the Memory Stick PRO has a maximum potential size of 32 GB. As of early 2008, Mark 2-certified versions of Memory Stick PRO Duo became available. The Mark 2 designation indicates the Memory Stick is suitable for use with AVCHD recording products by providing appropriate minimum write performance. 5. SD(Secure Digital) The SD card was developed by Matsushita, SanDisk, and Toshiba for use in portable devices. Today it is widely used in digital cameras, handheld computers, PDAs, mobile phones, GPS receivers, and video game consoles. Standard SD card capacities range from 8 MB to 4 GB and for high capacity SDHC cards 8 MB to 32 GB as of 2008. With a physical profile of 24 mm × 32 mm × 2.1 mm, the new card provided both an SDMI-compliant (Secure Digital Music Initiative), high-level of copyright protection and high-density memory capacity for the time. The new memory card format was designed to compete with Sony's Memory Stick format that was released in 1998.

Comparison to other memory cards: Although, the SD cards are based on the older MultiMediaCard (MMC) format, but have a number of differences: first, 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. Second, the SD cards typically have transfer rates in the range of 10-20 MBytes/s, but this is always changing, particularly in light of recent improvements to the MMC standard. And finally, most SD cards are physically thicker than MMCs. Then, SD is less open than CompactFlash or USB flash memory drives, which can be implemented for free 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 can, at least, be accessed freely using the well-documented SPI/MMC mode. 6.XD 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.

7. USB(universal serial bus) In information technology, Universal Serial Bus (USB) is a serial bus standard to interface devices. USB was designed to allow many peripherals to be connected using a single standardized interface socket and to improve the plug-and-play capabilities by allowing devices to be connected and disconnected without rebooting the computer (hot swapping).

In the current, the USB supports three data rates: • A Low Speed (1.1, 2.0) rate of 1.5 Mbit/s (187.5 kB/s) that is mostly used for Human Interface Devices (HID) such as keyboards, mice, and joysticks. • A Full Speed (1.1, 2.0) rate of 12 Mbit/s (1.5 MB/s). Full Speed was the fastest rate before the USB 2.0 specification and many devices fall back to Full Speed. Full Speed devices divide the USB bandwidth between them in a first-come first-served basis and it is not uncommon to run out of bandwidth with several isochronous devices. All USB hubs support Full Speed. • A High-Speed (2.0) rate of 480 Mbit/s (60 MB/s).

And of the experimental data rate: • A Super-Speed (3.0) rate of 4.8 Gbit/s (600 MB/s). The USB 3.0 specification will be released by Intel and its partners in mid-2008, according to early reports from CNET news. According to Intel, bus speeds will be 10 times faster than USB 2.0 due to the inclusion of a fiber-optic link that works with traditional copper connectors. Products using the 3.0 specification are likely to arrive in 2009 or 2010.