Clarification: Secure Digital (shortened as SD) refers to a kind of flash memory card found in a digital camera model for storing the image data. Perhaps this is also the most common kind of a camera memory card. The size of MMC and SD flash memory cards is similar and so does the technology used in these two types because a SD card follows a MMC card in term of the design, but you cannot use these two kinds of memory cars interchangeably not in all of current digital cameras. There are two other types of memory cards, including MicroSD and MiniSD memory cards, but these two types are often found in mobile phones, rather than digital cameras. If you want to make MicroSD or MiniSD work with a camera that only accepts SD cards, you will need to use an adapter.
The three manufacturers including Toshiba, Matsushita and SanDisk cooperated to make the SD cards in 1999. The shape of these cards is a little bit rectangular, with a corner cut at an angle of 45 degrees. The measurement of a SD card is 24 mm x 32 mm x 2.1 mm (equivalent to 0.94 inch x 1.26 inch x 0.08 inch).
Currently, thanks to the secure digital technology innovation, SDHC (SD high capacity) memory cards have been available for the higher storing capacities up to 4 gigabytes (GB) and even more. The storage of SD cards is just at 2GB. Several older versions of digital cameras using SD cards can’t work with SDHC memory cards.