Bits from Bill

Technology thoughts leaking from the brain of "Bill Pytlovany"

Thursday, December 06, 2007

Mysteries of SD Flash Cards Exposed

I used to backup my data to CDs, then DVD’s but now with the low cost of solid state memory I’m actually archiving data on postage stamp sized 2 GB cards.  Secure Digital Flash memory is also becoming the most popular storage for camera’s, PDA’s, mobile phones and Audio players.

Unfortunately, if you’ve been shopping for SD cards you’ll easily be confused about which one to purchase. For instance Kingston has Secure Digital, Secure Digital Elite Pro, Secure Digital Ultimate and Secure Digital High Capacity.  SanDisk has its standard SD memory, Ultra II, and SD Extreme III.

Secure Digital Logo Secure Digital  (  <= 2 GBs )
Below are current rates from Amazon. Read/Write are maximum speed when no fragmentation of data blocks is found. Sometimes speed is measured in 66x or 133x. x = the standard CD-Rom speed of 150kb/s.
Name                   Price        Read     Write           Warranty
San Disk 2 GB           $15            ?         ?                 5-year
Kingston 2 GB           $15          5 MB/s  1.5 MB/s        Lifetime
San Disk Ultra II        $30         10 MB/s   9 MB/s         Lifetime
Kingston Elite Pro 50x $27         8.2 MB/s  7.7 MB/s      Lifetime
San Disk Extreme III   $38        20 MB/s   20 MB/s        Lifetime

 Secure Digital High Capacity LogoSecure Digital High Capacity  ( > 2 GBs )
Speed is measured by class which is the minimum data rate even with fragmentation. In theory these cards could grow to 128 GBs although 8 GB is most currently available. While the higher capacity SD cards are typically formatted with the FAT32 file system that isn’t the difference between SD and SDHC. SDHC uses SD protocol 2.0 to store data blocks. 
Class   Speed
  2         2 MB/s
  4         4 MB/s
  6         6 MB/s

You might think price equals quality and speed but it’s a little more complicated. Many camera’s and other devices won’t support the larger SD cards. Many card readers don’t support the new SDHC format for cards over 2 GB. For instance, our grandson is getting a Kid-Tough Digital Camera from Fisher Price which doesn’t support “high speed” SD or cards greater than 1 GB.  The Nintendo Wii only supports up to 2 GB. Some devices may support new protocols if their firmware is updated. Not every store includes this very useful information in their product description.

One of the cool things about the SD type memory is its SDIO expandability. This allow devices to be built along with the card including wireless, cameras, GPS, fingerprint recognition and much more. I recently wrote about the Eye-Fi SD card which uses this functionality.

The big question for me is how many times can the memory be written to, and how long with it last?  This information isn’t easy to find. The industry claims this kind of memory( NAND) can be written to up to 100,000 times and operate up to 51 years.  My research concludes that SD memory should last up to 10 years when stored in a safe place.

What you really need to remember…

  • When purchasing SD cards make sure it’s compatible with your device and your SD reader and vise versa.

  • When writing data to your SD card, be sure the operation is complete before removing the card from the reader.

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Blogger Unknown said...


Thank you for the clarification. The SD Card Association website gave me that impression but I appreciate you taking the time to include the additional information for my readers. It appears that SD cards are here to stay so the more information the better.

Thanks again,

1:27 PM  

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