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MicroSD card speed for 4K video

Started 7 months ago | Questions thread
John Vickers Contributing Member • Posts: 911
Re: MicroSD card speed for 4K video

DMKAlex wrote:

Thank you for the in-depth explanation.

Very helpful.

You're welcome. I hope it helps a little.

A couple of minor things, for completeness.

The U1/U2/U3 and V30/V60/V90 are about the ability to sustain writing a lot of data in big chunks. Checking the sdcard specs, the "big chunks" used in testing seem to be 512kByte.

But in a phone or tablet, when the card is used for storing applications or application data, the important part of the performance may be how quickly the card can process lots of fairly small requests - such as 4kByte reads spread fairly randomly. 4kByte is the typical page size (memory allocation unit) for modern processors. It's too small to be optimum for modern processors, and probably should now be 16kByte, or even 64kByte, but that's another story.

There's another performance badge for that: A1/A2. It's about the minimum number of small (4kByte) requests the card can process.

SD Association: https://www.sdcard.org/consumers/about-sd-memory-card-choices/application-performance-class-for-running-smartphone-apps/

If you have an Android phone or tablet, it may require "A1" to allow apps to be stored on the card.

So, other things being equal, if you think that at some point the card might end up in your kid's phone, or one of you wives' tablets, A1/A2 rated cards may work a bit better.

SDcard "simplified" specifications, including partial descriptions of tests: https://www.sdcard.org/downloads/pls/ (The relevant doc is the "Physical Layer" spec).

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