SanDisk SDHC Speed versus Class Ratings Q&A

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SanDisk SDHC Speed versus Class Ratings Q&A

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Speed versus Class Ratings Q&A

Q: What’s the difference between speed and class ratings for SDTM/SDHCTM cards?

A: Still digital images shot on high-megapixel cameras should utilize fast data throughput (a large pipe), for improved results when writing and reading images to and from the card. The speed rating measures maximum transfer speed for writing and reading images to and from the card, expressed as megabytes per second. However, video doesn't need as big a pipe because the video format is a smaller "fixed stream" that uses only a portion of the pipe.

Unlike card write speeds that measure maximum performance, class ratings measure the minimum sustained speed required for recording an even rate of video onto the card. The class rating number corresponds to the transfer rate measured in megabytes per second. Class 2 cards are designed for a minimum sustained transfer rate of 2 megabytes per second (MB/s)1, while Class 10 cards are designed for a minimum sustained transfer rate of 10MB/s2.

Q: What are the benefits of a using an SD/SDHC card with a higher speed rating?

A: Using flash memory cards rated for higher speeds allows images to be written to cards faster, which reduces waiting time between shots and enables continuous burst mode on more advanced cameras. The faster speed is especially beneficial in capturing a series of fast-action images or human expressions and reactions. Using faster memory cards also provides quicker transfer of both still images and video files from the camera to a computer (an action known as read speed), so there’s less time spent waiting for files to offload from the memory card.

Q: What are the benefits of using an SD/SDHC card with a higher class rating?

A: Using flash memory cards with higher class ratings ensures that the video captured on the cards is recorded at an even, sustained rate with no dropped frames which typically results in lost data and choppy playback. A higher class rating is not always better for video recording because it must meet the camera’s specifications for minimum sustained transfer speed. However, using a card without the proper class rating on a more advanced camera, such as a high-definition (HD) camcorder or Digital Single Lens Reflex (DSLR) camera with HD video recording, is likely to result in an error message indicating that video can only be recorded at a lower definition setting.

Q: What card ratings are generally recommended for different types of cameras?

A: SanDisk Extreme SDHCTM cards3, which are currently rated up to 30MB/s, are recommended for DSLR cameras that take high-resolution images and provide continuous shooting mode or continuous burst mode. SanDisk Ultra SDHC cards, which are currently rated for 15MB/s read and 9MB/s write speeds, are recommended for high-megapixel, high-end digital point-and-shoot cameras. Users should match class ratings with the camera or camcorder manufacturer’s recommended specifications for video capture and playback. However, any camera or camcorder that captures high-definition video requires a minimum class rating of 4 or higher.
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