# SD Card Readers



## okuma (Jun 17, 2011)

For down loading files from a SDHC card, it it better/faster to use the integral card slot in the computer or purchase an external, portable card reader?
I assume the internal card slot would be limiting to the rate of the portable reader???


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## LouieSherwin (Jun 17, 2011)

Hi,

I suspect that they will be essentially the same so long as the external reader is attached using USB2. The through put is probably limited by the card I/O speed in both cases. Also the internal reader will be more reliable since you do not have a cable that can potentially go bad.

I just checked the HW configuration on my MacPro and the internal card reader was not as I thought connected through USB bus but has it's own independent driver. That could mean it is more likely to be able to read at the full rated speed.

-louie


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## Kiwigeoff (Jun 17, 2011)

If your card reader came with the computer it may not be the best quality.
Personally I use a Lexar Pro card reader and find it quick and reliable.


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## Jim Wilde (Jun 17, 2011)

Interesting. Just ran a simple set of tests, copying 5GB of CR2s from a 5DMkII (using a Sandisk Extreme Pro card rated up to 90MB/s), to the same internal hard drive on my desktop PC, using:

Direct connection from Camera using USB2 cable. Transfer speed was 27.4 MB/s.
CF card inserted into internal card reader. Transfer speed was 15.8 MB/s.
CF card inserted into external Sandisk USB2 card reader.Transfer speed was 24.6 MB/s.
A couple of surprises there. I didn't expect direct Camera connection to be the fastest transfer method, and I didn't expect the internal card reader to be quite as slow in comparison to camera and external reader.

So now I'll have to think whether the convenience of using the internal card reader outweighs the relative 'slowness'. Probably will for my volume of shooting, but I could imagine a high-volume shooter looking for quicker methods.


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## Mark Sirota (Jun 17, 2011)

Jim, did you run those tests multiple times?  You might find that caching is affecting your results.  If a second run immediately after the first is faster, then caches are coming into play.


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## Jim Wilde (Jun 17, 2011)

Good point, Mark. I'll retest in a different order....


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## Jim Wilde (Jun 17, 2011)

OK, reran the tests a couple more times for each device type, and results were consistently the same apart from the test direct from camera which slowed a touch from 27.4 MB/s to 26.2 and 25.8 MB/s.

Interesting that the cache seems not to influence this at all. During the copy, all the data appears to be written to the system cache (available memory consistently at zero throughout the whole test), BUT it seems as if the OS fails to recognise that it has the data cached for subsequent copies....perhaps the fact that the source was different, even though the data was the same, stopped it reading from the cache instead of the device?

So to test this I repeated one of the tests 4 times in succession, with a reboot in the middle to reset the cache, and got more or less identical timings. During the third run (the first after the reboot), I could see the cache being filled up, but the fourth run timing was no different. If I knew more I could probably explain it.....but I don't, and anyway this is a long way off topic now!


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## simonb (Aug 23, 2011)

Well that would not matter that much as they are looking to be attached on the same port which is a 2.0 I suppose.  Though there are some new 3.0 card readers out in the market and cnet is giving them quite a good rating though they are about $30 a piece.

I have not really tried them out yet so I cannot really say much about their performance.  The one cnet reviewed was Delkin.


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