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Memory + SD Cards

Former Member

So, I have been looking at at a few videos for this, and although I'm no expert, im certainly enjoying reading about it, and it seems like a massive breakthrough in... Well, every section of computing - there will be new operating systems for this at some point, maybe a new programming language that is unique to the Raspberry Pi, and of course it is redefining hardware.

 

My only problem is memory - i have been looking around, and i can't find any SD cards with more than 8GB memory, which fairly worries me, because i don't want to invest in an external harddrive for this. Am i not looking hard enough, or is this going to be our limit until the hardware for SD cards improves?
Also, if that is right, wouldn't it be easier, and more effective, to just use a memory stick and put it in a USB drive?

 

Thanks a lot,

Danny

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  • in reply to fustini

    I would like to apologize in advance for my ignorance.  However, I do have a few questions regarding the size and speed of the SD cards that we will be able to use.  I do understand that currently a list of compatible cards (and suggestions for cards that will not work) are listed here:

     

    http://elinux.org/RPi_VerifiedPeripherals#SD_cards

     

    What I do not understand, and hopefully someone will educate me, is why the class of the SD card really matters in regards to compatibility?  I thought all SD cards are built to a standard, meaning a SD card is a SD card, is a SD card.  The reason I am asking is that I would really like to use a 32Gb class 10 SDHC card that I have when I get my RbPi.  Is the incompatibility that is referenced something that can be fixed in firmware?

     

    Thanks!

    Macmuchmore

  • in reply to Macmuchmore

    Andrew,

     

    I'm not sure why the class entirely matters but a quick search of the differences in the classes turned up this link:

     

    http://www.buzzle.com/articles/sdhc-card-class-difference.html

     

    I'm not sure of the reliability of the source, nor if the info there means much to you. From there, it would seem that the differing classes relate to different transfer speeds. Perhaps the RPi has a hardware problem with the increased speed, or there is a software problem. It would seem the problem lies mostly eslewhere since they state that even among the same cards there could be problems depending on whether the design has been altered (even though the specs remain the same). Most likely, someone more knowledgeable about this will reply sometime soon and we can both learn image

     

    For now, I'd just say err on the side of safety and buy an SD card that you know will work. Then once more knowledge has been worked out (and hopefully software/firmware has been fixed of any bugs) many more cards will be easily usable and you could then pick a much larger card (they're fairly cheap anyway, and I'm sure it wouldn't been too difficult to find a use for the old card, I find it hard to assume that the only use of a spare SD card that you could find would be the RPi).

     

    I know it doesn't mean much, but I think we're pretty much all in the same boat. At least every item in question is cheap, it's hard to be patient though but should be worth it.

  • in reply to Former Member

    In the webinar yesterday, Eben says (at 43:20) that the problem with Class 10 cards

    is now understood to be a voltage issue, where the RPi uses a fixed 3.3v interface,

    but class 10 cards use a lower voltage.  He said that fixing this will require a hardware

    change, although there are no definite plans in place for such a change.

  • in reply to Former Member

    Re. SD card voltage,

     

    I find the "lower voltage" statement puzzling - I haven't done an exhastive search but I see no reason from the 10 minutes googling I have done for this to be an issue.

     

    http://www.dpreview.com/news/2012/03/14/Toshiba-Exceria-high-speed-SDHC-SDXC-UHS-I-cards

     

    These are some bleeding edge cards and all work with 3.3V

     

    I'll try some (need to get round to it anyway) in a system I'm working on (not an RPi) where I have access to all the registers and see how they fare. So far its only been tested with 4Gb cards and we need to try everything.

     

    Michael Kellett.

  • in reply to michaelkellett

    As promised, very quick test on 32Gb Class 10 card (Samsung 32Gb Micro SD, HC) from Amazon.

    Tested with ST ARM CortexM4 (STM32F407....) fixed 3.3V interface and power.

    Software Keil ARM RTX and RL-FlashFS using ST driver for the SD card (in 4 wire native mode)

     

    I didn't have time for serious speed tests but the boot up on this system works OK:

    image

    The same card works OK with a Windows PC using a £1.90 USB <-> SD card adaptor, Windows reports 29.2 Gb free.

    Not much of a test but I don't think fixed 3.3V should be  a problem.

    (It would be nice to be more definite about this but the full SD specification can only be obtained by paying serious money to join the SD card association and the publicly released simplified spec. is short on detail in this area - however it does not look as if 1.8V signalling is required by Class 10 cards.)

     

    Michael Kellett