Bus Speed (Default Speed/ High Speed/ UHS)

Bus Speed

For the sheer variety of high-performing, feature-rich devices, the SD Association introduced higher speed bus interface (I/F) and its Maximum writing speed specifications for SDHC memory cards and SDXC memory cards.

Bus Interface Card Type Bus Mark Bus Speed Spec Version
Normal Speed SD, SDHC and SDXC --- 12.5MB/s 1.01
High Speed SD, SDHC and SDXC --- 25MB/s 2.00
UHS-I SDHC and SDXC 50MB/s (SDR50, DDR50)
104MB/s (SDR104)

Maximum speed differs from the bus I/F speed. It varies depending upon the card performance. The average speed that a device writes to an SD memory card may vary depending upon the device and the operation it is performing. The speed may also depend on how other data is stored on the SD memory card.

Normal and high-speed cards can also be used with UHS-I host devices, but the high performance enabled by a UHS-I host device can only be achieved with a UHS-I memory card.

UHS-II Pin Layout

A new pin layout was introduced to support the UHS-II bus interface. The new second-row pins on the full-size SD memory card and microSD memory card are used for the UHS-II signals. The first-row pins are used for the normal speed, high speed and UHS-I bus interface signals to provide interoperability with existing non-UHS-II host devices.

Normal Speed/High Speed/UHS-I Card