Answer:
SM (SmartMedia) cards, CF (CompactFlash) cards, and similar types of removable storage media use flash memory technology. Unlike ordinary RAM found in PCs, which loses its contents when the power is turned off, flash memory continues to store its contents even when someone (or something) eliminates the power. Plus, there's no battery-operated power source needed to back up and maintain flash memory, which means memory cards are small and lightweight. Thus, users can easily move them among digital devices, such as cameras and printers. And hot swapping lets users insert and remove this type of media even when the host device is powered on.
There are two main types of flash memory: NOR and NAND. NOR flash chips are the better choice for high-speed random access operations (similar to RAM), and because of this, PDAs (personal digital assistants) and mobile phones often use them. NAND flash chips excel at moving large blocks of sequential data (such as photo image files) and are ideally suited for digital storage applications. As a result, most digital storage media is based on NAND flash technology.
There are several common types of flash memory cards. CF cards are about the size of a matchbook, include an IDE (Integrate Drive Electronics) interface, and have a very fast data transfer rate. SM cards, which look like a tiny floppy diskette, don't have a built-in controller, so the host device (the camera, for example) must provide the necessary circuitry to control the card. MMCs (MultiMediaCards) are about the size of a postage stamp, and you'll often find them used in digital cameras and MP3 players. SD (SecureDigital) cards appeared in 2001 as a successor to the MMC because they are faster and provide security features such as cryptography. |