Determining the speed of the SD card
To begin with, let's try to figure out what the characteristic is: speed class SD memory card (Speed Class).
The actual recording speed of different manufacturers may vary, but for recording streaming content (video for example), a constant minimum recording speed is important. The Secure Digital Association to help consumers choose memory cards that are suitable for their performance has defined the Speed Class speed standards.
When ordering memory cards from the sky, there are often doubts as to whether the class is asserted. The largest Chinese marketplace, alibaba, even advises checking speed using the free h2testw utility, some use the Crystal Disk Mark utility.
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Sometimes it happens that they do not reach the declared speed quite a bit and the person begins to resent that the Chinese have deceived him and sold the card in a lower class.
It seems that everything is simple, clear and obvious, but there is a nuance. The fact is that according to the specification when evaluating the performance of MB = 1000 × 1000 Bytes.
It became interesting, do these utilities take into account this feature of the assessment.
Crystal Disk Mark is an open source software program. A quick look at the source gave the result:
MB as it should be = 1024 2 bytes.
h2testw - the program is free, no source code was found, I had to dissect:
And in this program a megabyte block of 1024 2 bytes is expected.
As a result, due to the difference in the block size, in order to correctly classify the memory card, you need to add about 5% to the measured recording speed (1024 2/1000 2 = 1.049)
Source: www.sdcard.org
The actual recording speed of different manufacturers may vary, but for recording streaming content (video for example), a constant minimum recording speed is important. The Secure Digital Association to help consumers choose memory cards that are suitable for their performance has defined the Speed Class speed standards.
- Class 2 - performance is greater than or equal to 2 MB / s
- Class 4 - performance is greater than or equal to 4 MB / s
- Class 6 - performance is greater than or equal to 6 MB / s
- Class 10 - performance is greater than or equal to 10 MB / s
When ordering memory cards from the sky, there are often doubts as to whether the class is asserted. The largest Chinese marketplace, alibaba, even advises checking speed using the free h2testw utility, some use the Crystal Disk Mark utility.
')
Sometimes it happens that they do not reach the declared speed quite a bit and the person begins to resent that the Chinese have deceived him and sold the card in a lower class.
It seems that everything is simple, clear and obvious, but there is a nuance. The fact is that according to the specification when evaluating the performance of MB = 1000 × 1000 Bytes.
It became interesting, do these utilities take into account this feature of the assessment.
Crystal Disk Mark is an open source software program. A quick look at the source gave the result:
#define DISK_TEST_MAX_BUFFER_SIZE 1024*1024 BufSize = DISK_TEST_MAX_BUFFER_SIZE; result = WriteFile(hFile, buf, BufSize, &writeSize, NULL); MB as it should be = 1024 2 bytes.
h2testw - the program is free, no source code was found, I had to dissect:
And in this program a megabyte block of 1024 2 bytes is expected.
As a result, due to the difference in the block size, in order to correctly classify the memory card, you need to add about 5% to the measured recording speed (1024 2/1000 2 = 1.049)
Source: www.sdcard.org
Source: https://habr.com/ru/post/156253/
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