Joop Boonen wrote: > Yesterday I bought a SanDisk Mobile Ultra microSD 4GB class 6 it seems as > it was cheaper with an usb adaptor than a slower class2 version. > > I have a feeling that the boot processes if much faster than the boot > process with the supplied class 2 card.
There are multiple timing factors to consider, and the generic class designation is really just "marketing-speak". The transfer rate that we can get on the GTA02 is limited, and will be far less than the 25MHz max clock frequency (the same is true on the GTA01, although for different reasons). The kernel will tell you what speed it selected for the card at boot time. But that's just the speed at which the data is clocked in once its ready. The other factor is how long it takes from issuing the command to the card to fetch a block of data until that data is ready to be transferred in (latency). Nothing currently collects and displays this bit of data for the user, but it would be a very important factor in overall performance, and it seems logical that higher-quality, higher-speed cards should have better specs here. It would be neat if someone could work up a patch to collect and display a min/max and running average of the latency time as observed by the kernel, but in reality I think that a quick test with bonnie++ on the SD filesystem will provide a much truer picture of how the various cards perform on the various devices. Maybe someone should add such a page to the wiki for users to submit their test results with various brand cards? Mike (mwester) _______________________________________________ hardware mailing list [email protected] http://lists.openmoko.org/mailman/listinfo/hardware
