Classes

• As of the date of publication, SD cards, in all their varieties, fit into two categories: Ultra-High Speed Class and Speed Class. The UHSC is comprised of just one subclass -- Class 1 -- that's designed to facilitate large-scale, HD, real-time broadcast-quality video through ultra-high speed bus interfaces. The SC is made up of Classes 2, 4, 6 and 10, which interface with high-speed or normal-speed bus interfaces. Class 10 SD cards are designed for full HD and HD still consecutive recording at high-speed bus interfacing. Classes 4 and 6 SD cards are intended for HD video at normal-speed bus interfacing, while Class 2 cards are capable of standard-definition recording with normal-speed bus interfacing.
  
  

Types

• In addition to classes and physical dimensions, SD cards are distinguished by their type. Currently, SD cards are available in three categories: SD, high-capacity SD and extra-capacity SD. Each category contains SD, miniSD and microSD formats, except SDXC, which is comprised of SDXC and microSDXC versions. SD, miniSD and microSD cards offer up to 2GB of memory, while SDHC, miniSDHC and microSDHC cards provide between 2GB and 32GB. SDXC and microSDXC cards, the newest members of the SD family, offer between 32GB and 2TB of memory. Class 6 SD cards are produced in all SD card forms.
  
  

Physical Dimensions

• SD cards are available in several sizes, each distinguished by its standard, mini or micro physical dimensions. By virtue of the devices they are designed to interact with, SD cards are compact and lightweight in their design. SD, SDHC and SDXC cards are about the size of a postage stamp, measuring 0.9 inches wide, 1.3 inches long and 0.08 inches deep and weighing 0.07 ounces. MiniSD and miniSDHC cards measure 0.8 inches wide, 0.8 inches long and 0.06 inches deep and weigh 0.03 ounces and are about a third the size of SD, SDHC and SDXC cards. As the smallest of the SD card family, microSD, microSDHC and microSDXC cards are about the size of a fingernail, measuring 0.4 inches wide, 0.6 inches long and 0.04 inches deep and weighing 0.02 ounces.
  
  

Standards

• Regardless of its category or speed class, each SD card is produced in accordance with the specifications and standards established by the SD Association. The SDA is an international collaborative organization composed of more than 1,000 electronics-related companies throughout the world that oversees the development of SD technology. Currently, SD cards are used in more than 7,000 products worldwide.