C10 / U1 / V10
Each represents a 10 MB/s minimum under its own defined speed-class protocol. Similar numbers do not make the protocols interchangeable.
microSD selection guide
C10, U1, U3, V10, V30 and A1: what each mark actually tells you.
Speed marks answer different questions. Use the host requirement first, then match the relevant class and validate the complete workload in the device.
Decision rule
Do not select from the biggest symbol on the card. Select from the host’s supported standard, minimum sustained write need and access pattern.
Read the marks in separate families.
U3 / V30
Each represents a 30 MB/s minimum under its own protocol. The host must support the relevant bus and class behavior.
A1 / A2
Application Performance Class focuses on random I/O plus sustained sequential performance. A2 performance requires both an A2 card and an A2-compatible host. It is useful for app-like workloads, not a replacement for a video requirement.
UHS-I symbol
The Roman numeral identifies the bus interface. It is not the same as the U1 or U3 speed-class mark.
Use a three-input selection brief.
Record the exact device, controller, firmware and maximum supported capacity.
Identify the workload: sequential video, small random files, read-heavy media, updates or a mixed pattern.
Match the host-required class, then test recording, overwrite, restart, power interruption and full-card behavior.
What the label cannot confirm.
Endurance
A speed class does not state the total lifetime of the NAND or the card under your write workload.
Compatibility
A correctly marked card can still expose a host, firmware, file-system or capacity-limit problem.
Supply continuity
Marks do not define the approved supply configuration, traceability or repeat-order requirements. Confirm those separately for the project.
Method & sources
Use the method inside its stated limits.
Method: Standards explainer based on the public SD Association definitions linked below. It separates label families before applying host documentation and device testing.
Limitations: This page does not confirm which marks are available on a current YOULEN series or capacity. Confirm the exact product configuration in the enquiry and order.
Content owner: Shenzhen Youlen Electronics Co., Ltd. overseas B2B project. Reviewed and updated: 5 August 2026.
SD Association: Speed Class SD Association: Application Performance Class