Secure Digital (SD) is a flash (non-volatile) memory card format for use in portable devices, including digital cameras, handheld computers, PDAs and GPS units. As of fall 2007, SD card capacities include 8 MB, 16 MB, 32 MB, 64 MB, 128 MB, 256 MB, 512 MB, 1 GB, 2 GB, 4 GB, 6 GB, 8 GB, and 16 GB. Several companies have announced SD cards with 32 GB. Cards with 4-32 GB are considered high-capacity. SDHC.