• SD cards are small memory storage units.SD Card Toolbox image by Ron-Heidelberg from Fotolia.com
  
  People use SD memory cards to store data, movies, pictures and music. They are small and inexpensive, making them useful for holding files in cameras, MP3 music players and other portable devices. SD memory cards come in a variety of memory capacities, most commonly available in sizes ranging from 2 to 32 gigabytes, with newer advanced designs capable of storing 2 terabytes.
  
  

SD Cards

• SD cards are often used in video cameras, computers and other large devices requiring memory storage. They weigh about two grams and measure 32.0 mm by 24.00 mm.
  
  

MiniSD

• MiniSD cards can be found in mobile phones and other smaller electronic devices. They weigh less than two grams and measure 21.5 mm by 20 mm.
  
  

MicroSD

• Smaller than a miniSD card, microSD cards are also suitable for use in small devices like mobile phones. They measure 15 mm by 11 mm and weigh less than a gram.
  
  

SDHC

• SDHC cards are high-capacity memory units that can hold from 2 GB up to 32 GB, and are available for use in digital cameras, mobile phones and other portable devices. They measure 32 mm by 24 mm and weigh less than a gram.
  
  

SDXC

• The XC in SDXC stands for extended capacity. These memory cards can store 2 TB of data, which makes them especially useful for recording high-definition video and storing uncompressed RAW format photos. They measure 32 mm by 24 mm and weigh less than a gram.
  
  

Speed Ratings

• SD cards are rated according to speed classes denoting their minimum sustained writing speed. Class 2 is 2 MB per second, Class 4 is 4 MB per second, Class 6 is 6 MB per second, and Class 10 is 10 MB per second. UHS Speed Class 1 (Ultra High Speed) is 104 MB per second and applies to SDCH and SDXC memory cards.