Monday, March 26, 2012

What is Secure Digital Memory Card ?

Secure Digital Memory Card (SD card in short), is a kind of new memory device based on semiconductor Flash Memory technology. It is widely used at portable units, such as DC, PDA, and multimedia player. SD card is developed by Panasonic, Toshiba, and SanDisk in August, 1999. The size of it is just like a stamp, and it only weighs 2g. It has very large memory capacity, high speed data transmission rate, great flexibility, and excellent security.
SD card combines SanDisk Flash Memory control with MLC (Multilevel Cell) and Toshiba 0.16u, 0.13u NAND technology together in its 24mm * 32 * 2.1mm size. It connects with special driver through 9 pins port, and it needn't extra power to maintain the memorized information. It is a unified solid dielectric, and it does not have any movable part, so there is no need to worry about the damage of mechanical motion.

SD card is applied in the following mobile digital devices:
● Digital camera. Save photos and videos.
● Digital camcorder. Save photos and videos.
● PDA. Save all kinds of information.
● Mobile phone. Save photos, rings, music, videos, etc.
● Multimedia player.
SD card is mostly used in MP3, DV, DC, etc, and also in Notebook. The projected area is as big as MMC card, but a little bit thicker: 2.1mm. The capacity of SD card is much bigger, and the read-write speed is 4 times faster than MMC card. At the same time the port of SD card is compatible with MMC card port. Most of the SD port also support MMC card. At present the application of SD card is rapidly spreading and has a trend to predominate in the DC camera market. This year the development of SD card is very fast and it has threatened the market share of CF card. That is because the size of SD card is much smaller than CF card, and the gap of capacity, performance, and price between SD card and CF card is getting narrower. Recent years phones that support SD card have been popular in the market. Therefore the rapid growing of SD card is not accidental. The most important point is that MMC is compatible with SD card. This is one of the reasons why SD card can get so popular. However, in some production like mobile phone, SD card is not compatible with MMC card. The capacity of SD card varies from 8MB to 32GB.

The size of SD card is very small. Before buying it the consumer usually will not have much information about it. It is a little difficult to identify from the appearance. Here are some ways to identify the common brands SanDisk SD card: firstly, check the card to see if there is laser chatoyancy label on the front side of pack. And the label will change color with the different angles. Secondly, check the quality card of agency. The pack is plastic, and it is the same with the one just mentioned. But the "5 years guarantee" and Japanese on the right below have been changed to image.
Besides, you can also check that if there are any gaps on the bottom of the card. The number on the back pack of SanDisk SD card is unique, and can be inquired by telephone. It is said the enquiry system has not been built.

In 2006, the capacity of SD card varies from 8, 16, 32, 64, 128, 256, or 512 MB, to 1, 2, 4, 6, 8, (SDHC) GB. 

SD/MMC card has replaced SM card developed by Toshiba and becomes the most common digital memory card form of portable DC. In 2001, SM card takes 50% market share and then falls to about 40% in 2005 and keeps falling. Most of DC producers provide SD card support including Canon, Nikon, Kodak, Panasonic, and KONICA MINOLTA. Other three leading firms still insist to use their patent forms: Olympus and Fuji use XD card, and Sony uses Memory Stick. Besides, SD card has not penetrated into the DSLR market which CF card takes up the leading position. (D50 released by Nikon in 2005 support SD.) SD card is made by Toshiba by adding encryption technology based on MMC technology. As MMC card may be used to copy digital music by users, Toshiba adds this technology to make the music industry feel safe. It is similar to Sony's MagicGate. Theoretically digital copyright management can be added to encryption technology, but this function has not been used very often. Users can use SD card through a USB card reader on computer. Some new type computers have been installed with built-in card reader device. The newest invention is building USB port in SD card and leaving out the card reader. The design of SanDisk is adding a folding jacket to protect USB port. Though SanDisk is not the first firm to add built-in USB port, because of its important position, it still makes other firms to follow the trend. Actually SD mark is firstly used in an entirely different way: it is firstly used at "Super-Density Optical Disk". But this production of Toshiba suffers defeat in the battle of DVD form. That's why the "D" looks like "Disk". 

SD series memory card is authorized by SD card association after testing by SanDisk. Therefore almost all the paten right is hold by SanDisk.

Mini SD and Micro SD card
With the development of SD card storage technology, Mini SD and Micro SD card have shown up. 

Mini SD
Mini SD is developed by Panasonic and SanDisk. For the convenience of more users to change to use Mini SD, SanDisk has specially developed SD convert card. It can be used with SD card DC, PDA, and MP3 at the same time. Mini SD is only 37% big as SD card, but it still has the same read-write function and large capacity of SD card. It is compatible with SD card. Through the SD convert card it can be used as normal SD card.

Micro SD  
SD card association firstly brings T-flash into the subminiature storage card production family, and named it Micro SD. After the release of nail big Micro SD, the consumers are all amazed by it. And now many phones are using this kind of memory card. MMC micro and Micro SD rank together the smallest mini memory card in the world. With the super mini size and greater advantages, it can be used in all kinds of digital production and doesn't waste much space of products' inside design. It is so popular among the designers and helps to make exquisite digital life a lot.

Overwrite-protect switch
There is a switch at the right side of SD card: overwrite-protect switch. MMC card does not have this switch. When the switch is turned down, SD card is protected from overwriting, and the information on the card can be read only. When the switch is turned on, the card can be overwritten again. 

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