SD Card
Memory Cards · 7 specs
Direct Answer
The SD Card (Secure Digital) is the global standard removable flash memory form factor established in 1999 by Panasonic, SanDisk, and Toshiba (SD Association). Measuring 32.0 × 24.0 × 2.1 mm, it spans capacity generations from original SDSC (up to 2GB) and SDHC (up to 32GB) to SDXC (up to 2TB) and SDUC (up to 128TB).
Source: SD Association (SDA) Physical Layer Simplified Specification · Last reviewed Aug 28, 2026
Specs
| Governing Body | SD Association (SDA) |
| Physical Dimensions | 32.0 mm × 24.0 mm × 2.1 mm |
| Pin Configurations | 9 pins (UHS-I / Legacy) / 17 pins (UHS-II / UHS-III dual-row) / 19 pins (SD Express) |
| Capacity Standards | SDSC (≤2GB), SDHC (4–32GB), SDXC (64GB–2TB), SDUC (2TB–128TB) |
| Standard File Systems | FAT12/16 (SDSC), FAT32 (SDHC), exFAT (SDXC / SDUC) |
| Operating Voltages | 2.7V–3.6V (Standard) / 1.8V (UHS-I/II signal voltage) |
| Mechanical Features | Write-Protect slide notch (left edge), 45-degree polarized corner keying |
Physical Pin Evolution and Dual-Row Architecture
The standard full-size SD card originally used a single row of 9 recessed gold-plated contacts (1-bit SPI or 4-bit parallel SD bus). To dramatically increase bandwidth without breaking backward compatibility with older host devices, the SD 4.0 specification added a second row of 8 supplementary pins recessed behind the primary row, providing the Low-Voltage Differential Signaling (LVDS) lines required for UHS-II (312 MB/s) and UHS-III (624 MB/s).
Capacity Generations and File System Mandates
The SD standard has evolved across four distinct capacity tiers:
- SDSC (Standard Capacity): Up to 2 GB formatted in FAT16.
- SDHC (High Capacity): 4 GB to 32 GB formatted in FAT32 with sector-based addressing.
- SDXC (eXtended Capacity): 64 GB to 2 TB formatted in exFAT (introduced in 2009).
- SDUC (Ultra Capacity): 2 TB to 128 TB formatted in exFAT (introduced in SD 7.0 in 2018).