UHS Speed Class

The next speed class up is the UHS (Ultra-High Speed) Speed Class and it’s denoted with the “U” symbol. There are two ratings within the UHS Speed Class:

• U1 (UHS Speed Class 1): minimum write speed of 10MB/s
• U3 (UHS Speed Class 3): minimum write speed of 30MB/s

The UHS Speed Class is more commonly used nowadays than the Speed Class and many high-end cameras require at least a U3-rated memory card for many of its functions, such as recording high-resolution videos. The UHS Speed Class mainly refers to the minimum sustained write performance for recording videos and came about due to 4K-capable video recording devices needing faster write speeds. As a rule of thumb, 4K-capable recording cameras will usually require at least a U3-rated SD card.

What makes the U1 and U3 memory cards more advanced than those in the Speed Class are that they use one of two UHS bus interfaces:

• UHS-I: theoretical maximum transfer speeds up to 104MB/s
• UHS-II: theoretical maximum transfer speeds up to 312MB/s

Both U1 and U3 memory cards can utilise the UHS-I bus interface, but are not compatible with the UHS-II bus interface.

These UHS bus interfaces indicate the theoretical maximum read and write speeds, unlike the sustained write speeds of speed classes. The UHS bus interfaces are denoted by a Roman numeral “I” or “II” symbol on the front of the card. The bus speeds refer to the theoretical data transfer rate of the interface itself while a U3-rated SD card has its own sustained write speed of 30MB/s. For example, a UHS-I U3-rated card guarantees a write speed of 30MB/s but has the potential for a read and write speed of up to 104MB/s if used with a device that supports a UHS-I bus interface.

A UHS-II compatible card has a potential read and write speed of up to 312MB/s. The UHS bus interfaces are backwards compatible so you can use a UHS-II card in a device that supports UHS-I, but you won’t see the speed benefits of UHS-II as the card will default back to the lower specs of UHS-I. Both the card and bus interface must be fully compatible to experience the speed benefits.

Video Speed Class

The latest Video Speed Class was created to enable higher video resolution and recording features, such as multiple video streams, 360-degree capture, VR content, and 4K- or 8K-resolution videos. They’re usually denoted with the “V” symbol. There are five ratings for the Video Speed Class:

• V6 (Video Speed Class 6): minimum write speed of 6MB/s
• V10 (Video Speed Class 10): minimum write speed of 10MB/s
• V30 (Video Speed Class 30): minimum write speed of 30MB/s
• V60 (Video Speed Class 60): minimum write speed of 60MB/s
• V90 (Video Speed Class 90): minimum write speed of 90MB/s

The Video Speed Class is unique because it’s capable of utilizing both the UHS-I and UHS-II bus interfaces. V6 to V90 speed class memory cards can use the UHS-II bus interface, but the UHS-I bus interface can only support V6 to V30 speed class memory cards.

The Video Speed Class offers the fastest speeds available and is ideal for ultra-high-resolution videos, high-quality videos and multi-file recording in drones and 360-degree cameras. It supports HD formats up to 8K video in drones, 360-degree cameras, action cams and VR cameras.

You can find the best card for your hardware device by choosing the same speed class or higher than the one required for your device. For example, if your device requires a Class 4 memory card, you can use Speed Class 4, 6, or 10. If your device requires a UHS Speed Class 1 card, you can use UHS Speed Class 1 or 3. The same functionality applies to the Video Speed Class as well. Note, that using a higher-rated card that goes beyond the speed class requirement for a device will still work, but you won’t be experiencing the full benefits of the higher speed class since the device only supports the lower speed class.