Types of Memory Cards
There are 2 types of memory card format families Secure Digital (SD) and CompactFlash (CF). The SD format includes SD, SDHC, and SDXC cards. SDHC (SD High Capacity) and SDXC (SD eXtended Capacity) raise the maximum storage capacities of cards in this family significantly. They're also faster than regular SD cards. Note that these formats aren't backward compatible. This means you need to know the sub-type supported by your device. However, there are memory card readers that support all three standards. They all have smaller versions referred to as microSD, microSDHC, and microSDXC cards.
The CF format is older than the SD standard, and still used in high-end cameras. It offers the high write speeds needed for burst photography. CFast is a faster variant of CompactFlash, and more suitable for shooting high-definition videos and high-resolution photos. XQD is even faster than CFast, and some high-end DSLRs and camcorders support this format.