Secure Digital card
A Secure Digital card (or SD Card) is a kind digital storage device which uses Flash Memory to store files, generally photographs or multimedia videos. They have become a common item, which can be used in digital cameras, video recorders, voice recorders, smartphones, media players, and more.
There are a number of variations of SD cards. The most common variation is size, since they are available in doubling sizes up to triple digits of Gigabyte (GB) capacity. Cards used to be available with space measured in megabytes, but as technology improves and data continues to take more space, these have become obsolete. Even 1, 2, and 4 GB cards are becoming less popular. This is not the only variation, however. Another is in physical size, between standard SD, Mini SD, and Micro SD. Standard size cards generally offer greater transfer speeds, but take up more space. They are generally used in cameras and media recorders, as well as some older smartphones, such as the Treo. Micro SD cards (previously named T-Flash, then TransFlash) are better suited for smaller devices. Despite their slower speed, they have proven popular for smartphones, media players, and other small devices such as voice recorders.
Other improvements have been made to Secure Digital cards, so that there is now the common High-Capacity type SD card—these offer greater data transfer speeds. There are also multiple classes of cards. The higher the class, the greater the transfer rate. So far, the class number has been the transfer speed is Megabytes per second. Therefore, Class 2 offers 2 MB/s, Class 4 offers 4 MB/s, Class 6 offers 6 MB/s, and Class 10 offers 10 MB/s. Unfortunately, higher class cards are not reverse-compatible, although the readers are. This means that a Class 6 card will not work in a class 4 reader, but a class 4 card will work in a class 6 reader. This is the same for HC cards. standard can be read by HC, but HC cannot be read by standard.
The original SD card has become largely obsolete as it is, because of its limited capacity. However, the High-Capacity type has taken over almost seamlessly. Nonetheless, other alternatives have been released, Including xD media cards and MultiMediaCards (MMCs)