What is a Speed Class?: Standards for SD Card Data Write Speeds🌱

In a nutshell...

It is a standard that indicates the data write speed.This allows you to know how fast an SD card can write data.

In this article, we will introduce in detail the types of speed classes for SD cards, the supported pixel counts, and more✨

Types of Speed Classes

There are four types of speed classes: "Speed Class," "UHS Speed Class," "Video Speed Class," and "SD Express Speed Class."

The following is quoted from the website of the SD Association, which is the standards organization that defines industry standards for SD cards.

Background on the creation of four types of speed classes

Why are there four types of speed classes? This is because the types and amounts of data handled have changed with technological advancements.

In the early days of memory development, standard video (640×480 pixels) was mainstream, but later, HD/Full HD video (1920×1080 pixels) became the standard.

Currently, 4K video (3840×2160 pixels) and 8K video (7680×4320 pixels) have also appeared, and the amount of data being handled is increasing even further.

There is a high possibility that new speed classes will be created due to future technological innovation.

Details of each speed class

Here, we will explain the four types of speed classes in detail.

1. Speed Class

The speed class indicates the minimum guaranteed write speed per second and is classified as follows:

• Class 2: Minimum write speed of 2MB/s

• Class 4: Minimum write speed of 4MB/s

• Class 6: Minimum write speed of 6MB/s

• Class 10: Minimum write speed of 10MB/s

These classes are suitable for standard video recording and photography. For example, a Class 10 card is recommended when shooting Full HD video.

2. UHS Speed Class

UHS (Ultra High Speed) is a standard that provides higher write speeds than the standard speed class, and there are the following two classes:

• U1: Minimum write speed of 10MB/s

• U3: Minimum write speed of 30MB/s

The UHS Speed Class is suitable for 4K video recording and high-speed continuous shooting. Note that to achieve the guaranteed speed, both the SD card and the device being used must support the UHS Speed Class.

3. Video Speed Class

Like the Speed Class and UHS Speed Class, this is a standard that guarantees a minimum speed. It was established as a standard to meet the demands for high-resolution and high-quality video recording such as 4K and 8K, and it also supports next-generation flash memory such as 3D NAND. As of June 2024, there are the following five classes:

• V6: Minimum write speed of 6MB/s

• V10: Minimum write speed of 10MB/s

• V30: Minimum write speed of 30MB/s

• V60: Minimum write speed of 60MB/s

• V90: Minimum write speed of 90MB/s

These classes are suitable for 4K and 8K ultra-high-definition video recording.

4. SD Express Speed Class

The SD Express speed class is the newest standard for SD cards, announced in October 2023. This class was developed to support applications that require particularly high-speed data transfer.

SD Express achieves significantly higher speeds compared to conventional SD cards by adding PCIe (PCI Express) and NVMe (Non-Volatile Memory Express) interfaces to the SD card.
As of June 2024, there are the following four classes:

• E150: Minimum read/write speed of 150MB/s

• E300: Minimum read/write speed of 300MB/s

• E450: Minimum read/write speed of 450MB/s

• E600: Minimum read/write speed of 600MB/s

In addition to speed, power and temperature management are also specified, so if you are interested, please read this white paper.

Each speed class and corresponding pixel count

The range of pixel counts corresponding to each speed class can be summarized as follows.

Combination of host device and card

The memory card speed class is indicated on the packaging or manual of the host device (PC, game console, etc.). Because of this, it is necessary to use a card with equal or higher performance to record at the highest image quality or selectable image quality.

For example, if the host device requires an SD memory card with speed class 4, you can use an SD memory card with speed class 4, 6, or 10.

However, please note that you may not get the expected write speed with a combination of different marks.For example, with Class 10, U1, and V10, even if they show the same 10MB/sec write speed, the actual speeds may differ.

For this reason, it is important for users to choose a memory card with the optimal speed class according to the requirements of the host device. This allows you to maximize the performance of the device and record at the highest image quality.

What is the optimal SD card for use with the Nintendo Switch?

For official Nintendo Switch support, the use of a UHS-I microSD card with a read speed of 60-95MB/s is recommended.

It is a bit confusing, but both UHS Speed Classes U1 and U3 fall under UHS-I. The original text from the SD Association is provided below.

In other words, for Nintendo Switch use, it is clear that a speed class of at least U1 is desirable.

However, the Nintendo Switch does not support UHS-II, so using V60 or V90 SD cards is pointless.

From this, the following conclusion can be drawn.

For Nintendo Switch use, a microSD card that supports UHS Speed Class U1 to U3 or Video Speed Class V10 to V30 is optimal.

Summary

Speed class is an important indicator of SD card performance. By choosing the appropriate speed class for your intended use, you can optimize video recording and application performance.

Also, it is important for users to choose a memory card with the optimal speed class according to the requirements of the host device.

When using an SD card, please try to choose an appropriate SD card that matches the requirements supported by your device.

References

https://www.sdcard.org/pdf/SDExpressSpeedClassSD9_1Specification.pdf

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