Questions about UHS-1


I recently purchased a 64GB class 10 UHS-1 micro SDXC card which I plan to use in my Samsung Galaxy S3.  When I tried to benchmark it in my PC’s reader, I was surprised to find out that I was only getting about 9MB/sec read speed instead of the 28MB/sec some people were getting using crystaldiskmark…!  I was later told that the host device needs to be UHS-1 compatible in order to get the full speeds…still, I wonder, how could it test so slow if I can test a standard 8GB SDHC card at 22MB/sec read in the same reader?!  How does that make sense??  I asked Samsung directly and the S3 is not even UHS-1 enabled…Does this mean that everybody buying this card (64GB micro SDXC class 10 UHS-1) for their phones are wasting money?!  Because if the S3 is not UHS-1 compatible, I doubt any other phone is…

Would buying the same card but class 6 give better speeds in non-UHS-1 host devices?!

Good question, i’d also like to know this.

Has anyone got the SD Card Reader android app to test the speeds of a normal Class 10 card and a UHS-1 card?

I have similar questions.  It is very unclear what the differences are between various Sandisk MicroSD cards.

The 64GB MicroSD Ultra has several variants which all show “up to 30MB/s”:

SDSDQUA-064G-U46A - 64GB microSDXC Class 10 / UHS-1

SDSDQUA-064G-A11A - 64GB microSDXC Class 10 / UHS-1

SDSDQY-064G-U46A  -  64GB microSDXC Class 6

I have read in various forums that:

    1 - The class 6 is better for random read-write than the class 10.  Is this true?

    2 - They are all the same card, just the labels have changed.  Is this true?

    3 - They are the same card, but the formating is slightly different out of the box… but when reformatted, they all perform the same…True?

Any definitive answers here?



The card will work it will just work at a slower speed. The UHS cards will not however work at 30MB/s their Max speed will be more around 20MB/s in non UHS devices. UHS and non UHS product have different hardware and firmware. While they are backwards compatible they are not the same and the performance will differ slightly. 

the 2 class 10 UHS-1 cards are the same. the class 6 card was designed using SD 2.0 spec where the UHS class 10 cards were designed using the SD 3.0 spec. 

So, would the class 6 (SDSDQY) perform better than the Class 10/UHS-1 (SDSDQUA) for random read write?


@sgogo wrote:


I believe he is on vacation or out of town on business.


Some Android devices are having problems accessing Class 10 cards.  I use the 64GB Mobile Ultra Class 6 card in my ASUS Infinity Tablet and it performs fine.

What about using another filesystem on the card to boost the speed… one that android would recognize such as yaffs2, or ext4?

Has anyone tried htat to boost the speed of their drives?

And, I’m not understanding how a class-6 card on the sd2 standard can be faster than a class10 card on the sd3 standard.

I don’t doubt the results, but it doesn’t make sense and seems a little counter-intuitive.  Can anyone explain more?

what is the difference in write speed between:

* SDSDQUA-032G (MicroSD for Smartphone)

* SDSDQUI-032G (MicroSD for Camera)

* SDSDU-032G (regular SD)?

I’m looking for fast and good value cards for my camera (Panasonic mirrorless GX7), so it can be standard SD size but It’s nice to have the option to use the card in smartphone as well especially when it gets older. 

Will the microSD brothers match quality of SDSDU? 

Is there any difference between both MicroSD offerings or it’s only marketing positioning difference?

many thanks for the answer, and the Happy New Year! :slight_smile: