These are SD card shield. It provides a storage space for your Arduino. Users can read/write SD card via Arduino’s built-in SD library. It supports SD, SDHC and Micro SD cards.
Here lists the comparison between various versions of SD Card Shield:
|Parameter||SD Card Shield V3.0||SD Card Shield V4.0|
|SD Card Socket||Two Socket(SD Card Socket and Micro SD Card Socket)||a standard SD Socket(included adaptor enables using of Micro SD cards)|
|Supported Card Type||SD card(<=2G); Micro SD card(<=2G); SDHC card(<=16G)||SD card(<=16G); Micro SD card(<=2G); SDHC card(<=16G)|
|Compatibility||Do not compatible with Mega||Compatible with Mega|