SD Bus Interfaces vs. SD Speed Classes
Comparing 2 standards across 12 specifications. 12 key differences identified.
SD Bus Interfaces define the physical and electrical signaling architectures through which SD and microSD cards transfer data with host controllers. Spanning legacy Default/High Speed, Ultra High Speed tiers (UHS-I up to 104 MB/s, UHS-II up to 312 MB/s, UHS-III up to 624 MB/s), and PCIe/NVMe-based SD Express (up to 3,940 MB/s).
SD Speed Classes are standardized performance metrics defined by the SD Association to guarantee minimum sustained write speeds for uninterrupted video recording and random IOPS execution for applications. They encompass legacy Speed Class (C2–C10), UHS Speed Class (U1/U3), Video Speed Class (V6–V90), and Application Performance Class (A1/A2).
Specification Comparison Table
12 Parameters| Parameter / Spec | ||
|---|---|---|
|
Default Speed (DS) / High Speed (HS)
|
12.5 MB/s (25 MHz @ 3.3V) / 25 MB/s (50 MHz @ 3.3V) | — |
|
UHS-I (SD 3.01)
|
SDR12 (12.5 MB/s), SDR25 (25 MB/s), SDR50 (50 MB/s), DDR50 (50 MB/s), SDR104 (104 MB/s @ 208 MHz 1.8V) | — |
|
UHS-II (SD 4.0)
|
156 MB/s (Full Duplex) / 312 MB/s (Half Duplex) via 2nd pin row LVDS (0.26V) | — |
|
UHS-III (SD 6.0)
|
312 MB/s (Full Duplex) / 624 MB/s (Full Duplex dual-lane LVDS) | — |
|
SD Express (SD 7.0 / 8.0)
|
985 MB/s (PCIe 3.0 x1), 1970 MB/s (PCIe 4.0 x1 / 3.0 x2), up to 3940 MB/s (PCIe 4.0 x2) | — |
|
SD Express Protocol Stack
|
PCI Express (PCIe) + NVM Express (NVMe v1.3/1.4) over SD pins | — |
|
Speed Class (Legacy C-Class)
|
— | Class 2 (2 MB/s), Class 4 (4 MB/s), Class 6 (6 MB/s), Class 10 (10 MB/s) |
|
UHS Speed Class (U-Class)
|
— | U1 (10 MB/s min sustained write), U3 (30 MB/s min sustained write) |
|
Video Speed Class (V-Class)
|
— | V6 (6 MB/s), V10 (10 MB/s), V30 (30 MB/s), V60 (60 MB/s), V90 (90 MB/s) |
|
App Performance Class A1
|
— | 10 MB/s sequential, Min 1,500 Read IOPS, Min 500 Write IOPS |
|
App Performance Class A2
|
— | 10 MB/s sequential, Min 4,000 Read IOPS, Min 2,000 Write IOPS (requires Command Queue & Host Cache) |
|
Guaranteed Metric
|
— | Minimum sustained sequential write speed on fragmented NAND (never peak burst speed) |