Gadget Bag: SDHC Memory Cards

Secure Digital memory cards are becoming more popular in all sorts of cameras, and as maximum limits approach terabyte capacities, the format is poised to be the mainstay for still and HD video shooting in the future
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Despite strong competition from CompactFlash, the Memory Stick family and xD Picture Cards, the Secure Digital High Capacity memory card format—known as SDHC, for short—leads today’s popularity parade for digital image storage. Recent advancements in performance, the development of compatible derivatives and the industry-wide adoption of speed standards are working together to assure SD’s continued reign as the top-selling card.

First-generation SD cards offered storage capacities up to 2 GB, but that barrier was shattered with the introduction of SDHC, which pushes the upper limit to 32 GB. SDXC (see the sidebar) promises internal architecture that will support up to 2 TB—that equals 1,000X greater density than the original 2 GB limit.

In addition to higher capacities, SDHC offers other advantages. Before SDHC, cameras couldn’t determine the storage conditions inside the card when writing data. Writing throughput is heavily dependent on card fragmentation—the availability and arrangement of empty storage space greatly influences performance. With SDHC, devices designed to take full advantage of the standard can check the fragmented state in the card and calculate the write speed at every storage location. This means they can determine where to write the data according to its speed requirement.

SDHC is similar in appearance to MMC (multimedia cards), and many cameras that use modern SDHC also can use MMC or original SD—but not vice versa! You can’t use an SDHC card in an older camera that was built to use SD. Ditto for card readers, and that’s an important point because when you step up from a 2 GB SD card to an 8 GB SDHC, be sure to upgrade to a compatible Hi-Speed USB or SDHC card reader, too.

All SDHC cards that conform to the rules of the SD Card Association are marked according to their performance class. For example, Class 2 cards (the slowest) must deliver sustained read and write speeds of at least 2 MB per second (MB/s). Class 6 equates to 6 MB/s. The speed-rating system makes it easier for consumers to select the right card for a particular application, particularly video recording. There’s still some confusion, however, because some cards are capable of higher burst rates and are promoted as such. The key spec is sustained read and write speed—that’s the one that determines the speed class rating.

Camcorders that use SDHC—and there are many, many of them—have different requirements than typical digital cameras, and memory card manufacturers have fine-tuned their approach to that market segment. Because camcorders deliver a continuous stream of data to the memory card, the card must be capable of flawlessly sustaining read and write speeds of at least 4 MB/s. These are known as Class 4 SDHC as explained above.

Savvy card makers have designated certain cards as “video cards” and labeled them to match their videotape counterparts. Consequently, we find some Class 4 cards marked “4 hours” in addition to “16 GB.” We also encounter Class 2 cards labeled as “netbook cards” because small PCs typically don’t require cards capable of high-speed data transfer. Add this all together, and the result can be confusing; it’s possible to see two or even three cards from the same manufacturer—and of the same capacity—being sold for wildly different prices. In most cases, the difference is the speed class.

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Delkin 32 GB

Delkin Devices is a brand known for a wide range of digital camera accessories, including high-quality eFilm SDHC memory cards. Available in capacities up to 32 GB Class 6, all offer faster burst rates. Delkin Devices also markets a potent 16 GB Micro SDHC card. Aimed toward the GPS and cell phone market, the Micro SDHC can be used in any SDHC application via the included full-sized SDHC adapter. Also check out the Delkin Devices eFilm Reader-38, a USB 2.0 card reader that accepts 18 different memory card formats, including SDHC and its variants.

Hoodman RAW 16 GB

Hoodman RAW memory cards are made in the USA and offer a lifetime limited warranty. Available in 4 GB, 8 GB and 16 GB Class 6 capacities, they’re the only brand of memory cards that are advertised to be “lead free.” Although the name is RAW, in this case that’s an adjective Hoodman uses to describe their cards’ speed. Like all other SDHC cards, they can read and write any digital image or video file format.

Kingston 32 GB

As one of the world’s largest manufacturers of memory, Kingston Technology has built a fine reputation in the professional community based on high quality, broad variety and reasonable pricing. Kingston offers SD and SDHC cards in all sizes and speed classes up to 32 GB, and all Kingston memory cards are backed by a lifetime warranty and 24/7 technical support.

Lexar 16 GB

Lexar has been a staple supplier of SDHC cards since their introduction and offers a complete lineup in all sizes and performance categories. Labeled “Full-HD Video,” the 16 GB Class 6 SDHC card allows you to record up to six hours of HD video and includes exclusive, money-saving offers on leading Adobe software. The recently announced Lexar Professional 133x SDHC memory card now offers the maximum Class 10 speed rating, providing minimum sustained write speed capability of 20 MB/s for shooting higher-resolution images and high-definition video.

Panasonic 32 GB

Panasonic offers Class 10 Gold Series cards in 8 GB, 16 GB and 32 GB capacities. The 32 GB capacity card is able to store approximately eight hours of 1440x1080i high-definition video and more than five hours of 1920x1080i full high-definition video. Of equal interest to those on a budget is Panasonic’s Silver Series. These Class 4 cards are plenty fast enough for compact digital cameras and most camcorders, and are built to the same exacting standards, but are priced much lower.


PNY has been in the memory game since 1985 and has operations in 13 locations worldwide. They’re a leading manufacturer and supplier of high-capacity Flash memory cards, USB flash drives, solid-state drives and computer memory upgrade modules, as well as consumer and professional workstation graphics cards. PNY offers photographers a very wide range of microSD, SD, SDHC and other Flash memory cards and some of the most advanced professional-level graphics display adapters available, the PNY Quadro lineup.

SanDisk 32 GB

SanDisk is the world’s largest manufacturer of Flash memory storage products, and that alone says a lot. They’re widely acknowledged as the originator of Flash media. SanDisk is the only company that has the rights to manufacture and sell every major type of flash card. SanDisk was also the first company to recognize the need to clear the confusion consumers face when trying to match the right card to a specific application or device. To that end, they originated the video-packaging concept with the SanDisk Video HD card line. Available in SDHC (and Memory Stick PRO Duo), the cards are labeled to indicate minutes of video-recording time in addition to raw capacity.

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Transcend 16 GB

To date, Class 10 is the fastest speed available. Transcend has been in the memory business for 20 years and offers a full line of memory modules, USB flash drives and portable hard drives, MP3 players and other multimedia products—including their Ultimate Class 10 SDHC cards, with storage capacity up to 16 GB. In addition, they provide even higher burst rates of up to 16 MB/s write speed, making them ideally suited to shooting full HD 1080p video.


One thousand times more capacity than SD—and a faster data-transfer rate—that’s what SDXC promises. The new standard, announced in April 2009, increases SDHC storage capacity from 32 GB up to 2 TB, and increases bus interface speed up to 104 MB/s as of this writing (with a road map indicating a potential of 300 MB/s in the future). Theoretically, a 2 TB SDXC memory card could store about 480 hours of HD recording. And, the faster bus speeds will allow an increase in the number of frames per second, assuring even greater improvements in overall video quality.


What Exactly Does 133X Mean?
Before the adoption of standardized performance class ratings, card manufacturers used a speed-rating system borrowed from the original CD-ROM. First-generation CD players transferred data at 150 KB/s, the speed that represented the baseline of 1X. A CD player that was 4X could transfer data at 4×150 KB, or 600 KB/s. Play that out to modern SD cards, and you find that a 133X card offers burst speeds of up to 133×150, or 19,960 KB/s. While that sounds confusingly similar to the 20 MB/s promised by a Class 20 card, the hitch is that those speeds are burst speeds, not sustained speeds. It’s not uncommon to find a Class 6 card that’s capable of 20 MB/s for a brief period.


Delkin Devices
(800) 637-8087

Hoodman USA
(800) 818-3946


(800) 789-9418

(800) 211-PANA

PNY Technologies