SD and SDHC cards are flash memory cards.
Secure digital (SD) cards and secure digital high capacity (SDHC) cards are flash memory cards used for portable data storage. The two types of cards are exactly the same size. However, the card types are not necessarily compatible with the same devices.
Capacity
SD cards can hold from 8 MB up to 2 GB of data. SDHC cards can store 4 GB to 32 GB.
Speed
SD cards have a clock speed of up to 25 MHz per second. SDHC clock speeds can be as high as 50 MHz per second.
Data Transfer Rate
SDHC cards can read data at up to 95 MB per second and write data at up to 80 MB per second. SD cards can read data at up to 20 MB per second and write data up to 6 MB per second.
Compatibility
Devices designed to read SD cards will not be able to read SDHC cards. SD cards use a filing system known as FAT (File Allocation Table) 16. FAT16 allows up to 16 characters in file names. SDHC uses a FAT32 filing system. Since the file names are far longer than those allowed by FAT16, devices formatted for FAT16 cannot read the longer file names. Therefore, SD card readers are incompatible with SDHC technology. However, SDHC card readers are backwards compatible and will read SD cards.
Tags: SDHC cards, data second, file names, write data second, card readers, cards flash, cards flash memory