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SD class?

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james.knott at rogers

Jan 22, 2008, 7:13 AM

Post #1 of 3 (369 views)
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SD class?

I've notice a few messages about SD card class 4 & 6 etc. What's the
highest class that the N800 can benefit from? For example, will a class
6 device perform better than a 4? Or will the N800 be the limiting factor?

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dufkaf at seznam

Jan 22, 2008, 9:10 AM

Post #2 of 3 (352 views)
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Re: SD class? [In reply to]

James Knott wrote:
> I've notice a few messages about SD card class 4 & 6 etc. What's the
> highest class that the N800 can benefit from? For example, will a class
> 6 device perform better than a 4? Or will the N800 be the limiting factor?

Well, first it is good to know that this SD speed class thing is only
about writing. Reading is usually fast enough and above N800 limits.
Even class 2 card can do 16MB/s when reading with good USB card reader.
In N800 the limit is approx 7MB/s at default 24MHz SD/MMC clock rate.
With high speed (48MHz) mode enabled in kernel it can do approx. 11MB/s.
Both are read speeds, write speed limit is slightly lower. Also the
speed class is about guaranteed _minimum_ speed when writing
continuously. Average or normal speed can be higher. With my class 4
card I've seen higher write speed than 4MB/s.

IMO higher class is not worth extra money unless the difference in price
is small or you plan to write to the card often (like dumping hundres
of megabytes there regulary).

Frantisek

BTW, more details can be found also in
http://www.sdcard.org/about/memory_card/pls/Simplified_Physical_Layer_Spec.pdf
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mflaig at pro-linux

Jan 23, 2008, 12:54 AM

Post #3 of 3 (349 views)
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Re: SD class? [In reply to]

Hi,

5 minutes ago a package came containing a 4 GB sdhc class 6 card. I just
put it in the n810 and it works, so class 6 is the way to go (it was
just a few euros more than the class 4 sd card:)

Need to test it with the n800, but should be the same type of cards
supported - will test later, have to move to work now.

cya,

mflaig

On Di, 2008-01-22 at 10:13 -0500, James Knott wrote:
> I've notice a few messages about SD card class 4 & 6 etc. What's the
> highest class that the N800 can benefit from? For example, will a class
> 6 device perform better than a 4? Or will the N800 be the limiting factor?
>
>
>

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