SD cards come in three compatible sizes, as follows:

• MicroSD (15 mm × 11 mm)
• MiniSD (21.5 mm × 20 mm)
• SD (32 mm × 24 mm)

SD cards provide large-capacity storage in a tiny package with very low power draw, which is crucial because SD cards are often used in battery powered devices. SD cards also provide a broad range of storage capacity - from a paltry 16 MB at inception to the current maximum of approximately 32 GB. However, the next generation of SD cards, known as SD eXtended Capacity (SDXC), holds up to 2 TB (2000 GB) of data. SD data transfer speeds range from 2 MBps to approximately 90 MBps. By default, SD cards use the File Allocation Table (FAT) family of file systems (FAT16, FAT32, exFAT).

A key SD card feature is that it may be transferred between compatible devices. For example, vacation photos may be transferred from a digital camera to a PC. After inserting the camera's micro-SD card into the PC's corresponding slot or adapter, the PC recognizes the card as a new drive.

The SD format is governed by the SD Association - a global consortium of manufacturers.