Secure Digital (SD) is a non-volatile memory card format developed by the SD Card Association (SDA) for use in portable devices. The SD technology is used by more than 400 brands across dozens of product categories and more than 8,000 models.

At the 2006 International CES, the SD Card Association (SDA) announced their establishment of the SD Specification Version 2.0 for the SDHC (Secure Digital High Capacity); making way for the SDHC memory card to be the next generation SD Card. Engineered to meet higher memory capacities, the SDHC memory card will meet the higher requirements in a new generation of technology that enables SD cards to reach higher capacities of 4GB to 32GB. New electronic devices that will utilize SDHC memory cards include audio/video and telecommunications gadgets such as digital cameras, camcorders, mobile phones, computers, PDAs, plasma televisions, and many more.

SDHC memory cards are flash memory cards with a minimum capacity of 4GB. SDHC memory cards are designed for devices that are compatible with the SDHC 2.00 specification. Products designed exclusively to support previous SD specifications 1.0 and 1.1 will not be able to utilize SDHC memory card.

The growing demand for high-capacity flash memory springs partially from the increasing use of high-definition video and high-resolution digital photography. SDHC memory cards meet the challenge of these demanding products not only by providing ample storage but also by introducing a new feature: classifications of data transfer speed (DTS). Consumers can get the best performance value out of their digital products by using flash memory cards that support the device's highest standards for data transfer speed.

The SDHC memory cards are of different classes like Class 2, Class 4, Class 6 and Class 10.
SDHC memory cards are classified to guarantee a specific sustained DTS. This potentially saves consumers money, as flash cards are priced not only according to capacity, but also to speed. For example, if a product's maximum DTS is 2MB/sec, dishing out extra cash for Class 4 or Class 6 SDHC memory cards would be a waste of money. Conversely, devices that can utilize the 4MB/sec or 6MB/sec DTR will perform significantly better with Class 4 or Class 6 SDHC memory card, respectively.

Secure Digital was forced to create a new specification for SDHC memory card, when the previous specification topped out at a capacity of 2GB. This occurred previously when SD cards hit the 512MB wall. The new 2.00 specification should last a bit longer, as it allows SDHC memory card to reach a maximum capacity of 32GB. Secure Digital is so-named because of its ability to protect copyright content through digital rights management or DRM. Because of this, it is a favoured flash memory format in the audio-visual industry.

For greatest performance, users should pair their devices with the corresponding SD memory card. Your device's user manual will help you select a memory card built to the same SD standard as your device to maximize your device performance.