The Difference Between SD & SDHC Memory Cards

by Steve McDonnell

The Secure Digital memory card standard ensures interoperability among devices. It's supported by most small electronic devices that use memory cards for storage. A regular SD card uses the first version of the standard, which limits its maximum storage capacity. SDHC cards, which use a later version of the standard, can store more data and may also support ultra high-speed data transfer rates that a regular SD card does not support. SD standards are only backward compatible, which means that an SDHC card may not work in every device or card reader that supports the SD standard.

SD Cards

SD and SDHC cards are memory cards you can use to store files, music, pictures, video and any other data. Panasonic, SanDisk and Toshiba initially created the SD standard, which defines memory card specifications such as size, capacity, speed, security and power. SD and SDHC cards are typically used with small electronic devices such as cameras, cell phones and tablets, and can be read by laptop and desktop computers with a compatible card reader.

Capacity and Format

The primary differences between an SD card and an SDHC card are maximum storage capacities and default file format. A standard SD card is manufactured in versions that store up to 2GB of data using FAT16 as the default format. An SDHC card is manufactured in versions that store from 4GB up to 32GB of data using FAT32 as the default format. Both types of cards come in three different physical sizes: full SD, mini SD and micro SD.


SD standards are backward but not forward compatible. This means that a device that supports only the SD standard cannot read or write to an SDHC card, but a device designed for SDHC cards can read and write to an SD card. The SD extended capacity, or SDXC, standard supersedes SDHC. SDHC devices can't read or write to SDXC cards, but SDXC card readers can read and write to both SD and SDHC cards.


The SD card you use with a video recorder has to save data at least as fast as the recorder streams it. Higher video resolutions stream more data per second. SD cards have a speed class rating that defines how fast the card saves data. SD and SDHC cards may have a speed class rating of 2, 4, 6 or 10, where 2 is slowest and 10 is fastest. Speed class 1, also called Ultra-High Speed is the fastest. UHS did not exist when the SD standard was created and is only available with SDHC and SDXC cards.


About the Author

Steve McDonnell's experience running businesses and launching companies complements his technical expertise in information, technology and human resources. He earned a degree in computer science from Dartmouth College, served on the WorldatWork editorial board, blogged for the Spotfire Business Intelligence blog and has published books and book chapters for International Human Resource Information Management and Westlaw.

Photo Credits

  • David Paul Morris/Getty Images News/Getty Images