About the size of a US postage stamp, a Secure Digital High-Capacity (SDHC) card is a flash memory device that can hold between 4 and 32 gigabytes (GB) of data. These cards are a form of removable memory that can be used with many different digital devices, including camcorders and computers. While there are several other SD card products available, typically only machines that are labeled as working with SDHC cards can use them.
SDHC cards store and transfer information from one compatible machine to another. Many different types of devices, from digital cameras to music players to photo sharing products, made by most different manufacturers have slots that accept these cards. SDHC cards are perhaps most popular for recording and transferring media — including audio, video, or still pictures — from a camera or recorder to a computer so that they can be stored or manipulated. These storage devices function like many others: users can copy and paste files to the card, save files to it directly, or extract information from it.
Classifications and Storage
SDHC cards were designed to be an improvement on the original Secure Digital (SD) memory card developed in 1999. The new card helped satisfy the growing demand for high-capacity storage caused by the increasing use of high-definition video and high-resolution digital photography. SDHC cards also offered a new benefit for consumers: classifications of data transfer speed (DTS). Manufacturers categorize these products according to the minimum sustained DTS, grouping cards into four different classifications:
- Class 2: minimum sustained DTS of 2MB/sec
- Class 4: minimum sustained DTS of 4MB/sec
- Class 6: minimum sustained DTS of 6MB/sec
- Class 10: minimum sustained DTS of 10MB/sec
Cards in higher classes can transfer data more quickly in most cases, although this can depend on the card reader. The classes also are set by the minimum DTS, not the maximum, and a user may get much better performance. It's best for the user to test the writing speed of his device and use the recommended class, however, because this performance can be critical for users.
Choosing a Class and Capacity
Cards in the higher classes are useful for people who want to record high definition (HD) video or save many high resolution photos. Someone trying to record high definition video onto a slower memory card, for example, may find that he does not get the quality he expects, if the video records at all. Most experts recommend Class 6 for HD purposes; its speed is typically fast enough for most recordings and it's less expensive than a Class 10 card. Standard SD or SDHC Class 2 is usually fast enough for standard definition recording.
A 32 GB card can hold 4,161 22-megapixel photos compressed or 416 photos of the same size and quality uncompressed. When it comes to video, this same size card can hold 60 two-hour videos shot at 30 frames per second (fps). Users should make sure that their camera or camcorder can handle this amount of storage, however, because some inexpensive devices cannot be used with high capacity cards.
Most devices are designed to read a specific type of memory card or other storage method that is the current industry standard, along with many of its predecessors of the same technology, provided they are still available for sale. The opposite is not true, however; most older products cannot read memory cards made with newer technology. In other words, machines that have SDHC card slots can usually use this standard as well as the earlier SD, but those with SD slots typically cannot read SDHC cards. As a result, some companies have created software patches to allow older devices and the newer cards to work together, or made external readers that could be attached through a USB port.
If a product manual does not specifically list high capacity cards as a type of memory that can be used or says that the device is SD specification 2.00 compatible, it cannot use an SDHC card without an external reader. A newer card technology, called SDXC, is also on the market, and most products that accept SDXC cards will also read SDHC cards. Despite this, SDHC-specific devices may not be able to read an SDXC card or usability may be limited.