Why do SD cards show C10, U3, V30, and 95MB/s at the same time?
Asked 8/22/2018
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2 answers
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I'm comparing SD cards and I'm confused by the different speed markings. For example, one card is labeled C10, U3, V30, and 95MB/s. A speed-class chart makes U3 and V30 look equivalent, but C10 is lower, and 95MB/s seems much higher than any of them. Are these ratings contradictory, or do they refer to different kinds of speed?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
7y ago
2 Answers
4
The speed mentioned on the card is for reading information, not writing. All the marks (C10, U3, V30) are related to write speed. If you check the specifications of this SD card you will see few things which will change the numbers...
- The write speed (burst) is slower, around 90MB/s
- For SanDisk MB=1000000 bytes, which make speed around 85 megabytes/s
- You need SDXC compatible device to reach this speed
- All those speeds are: "Based on internal testing"
Originally by user34947. Source · Licensed CC BY-SA 4.0
user34947
7y ago
0
Generated from our catalog & community — verify before relying on it.
They’re not contradictory—they describe different speed measures.
- C10, U3, and V30 are minimum sustained write-speed classes.
- C10 = at least 10 MB/s sustained write
- U3 = at least 30 MB/s sustained write
- V30 = at least 30 MB/s sustained write for video use
A card can exceed those minimums and still only be labeled with the highest class it is certified to meet. So a card that can sustain 30 MB/s qualifies for C10, U3, and V30.
- The 95MB/s printed on the card is typically the maximum read speed, not the sustained write speed.
- Some specs also list a higher peak or burst write speed (for example, around 90 MB/s), but that may only be for short periods and not long enough to qualify for V60 or V90.
So the key difference is:
- Class symbols = guaranteed minimum sustained write performance
- Big MB/s number = usually best-case maximum read speed
That’s why one card can legitimately show all of those markings at once.
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UniqueBot
AI7y ago
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