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SD Card Class & Write Speed


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Old 03-05-2013, 23:54
wbm00
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Join Date: Dec 2011
Posts: 119

Hello

I have two class 4 SD cards and one class 6 card. Used a small app called Disk Bench from CNET Downloads to test the read and write rate.

The reason for doing these tests is because I noticed that in the same camera, the Play.com card won't have any issues whereas the video recorded on the Transcend 4GB lags every few seconds. I formatted the Transcend card but it didn't yield a result.

Transcend 4GB SDHC (Class 4)
Size: 151509532
Time: 45886 ms
Transfer Rate: 3.149 MB/s (writing)

Size: 151594212 bytes
Time: 11975 ms
Transfer Rate: 12.073 MB/s (reading)

Play.com 4GB SDHC (Class 4)


Size: 151509532
Time: 36441 ms
Transfer Rate: 3.965 MB/s (writing)

Size: 185444284 bytes
Time: 13952 ms
Transfer Rate: 12.676 MB/s (reading)

Transcend 8GB SDHC (Class 6)


Size: 151509532
Time: 38094 ms
Transfer Rate: 3.793 MB/s (writing)

Size: 118504372 bytes
Time: 9355 ms
Transfer Rate: 12.081 MB/s (reading)
As I understand it, class 4 should be a minimum performance of 4MB/sec and class 6 should be a minimum of 6MB/sec.

I'd be interested on what you experts think of the above stats. It seems to me the Transcend cards are underperforming, especially the class 6.
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Old 04-05-2013, 08:46
flagpole
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Join Date: Jan 2003
Posts: 43,524
You are quite right a class 4 should have a sustained write speed of 4MBs.

But the labelling, particularly at the budget end is a bit hit and miss. the write speed will depend on other things too, like how large the file is, how full the disk is., how it's formatted.

3MBs which equates to 24Mbs is the data rate for 1080p video on the iPhone 5, as an example. so it should still be sufficient for most video writing.

for my money. you can pick an 8GB class 10 for about 7.50
http://www.amazon.co.uk/Sandisk-Ultr...ds=8gb+sd+card
so i would just do that. infact a 32GB class 10 is only 18quid, a 16GB is 11quid
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Old 04-05-2013, 22:42
Helmut10
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Join Date: Dec 2011
Posts: 441
Looks like a Card Reader limitation, which is why you are seeing more or less the same from all of them.
You are testing both together not just the Cards themselves.

Try looking up the read/write speeds of your Card Reader.
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