[maemo-users] SD class?

From: Frantisek Dufka dufkaf at seznam.cz
Date: Tue Jan 22 19:10:14 EET 2008
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).


BTW, more details can be found also in

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