Curious behavior of a micro-sd card

May 14, 2007 9:48 AM

Odd problem with a micro-sd card. I was writing +-400 files to the root of it (under winxp) when after +- 10x files I got a "remove write protection" error , I couldn't write more files to card. I moved all of them to another just-made folder in the card. Now I can add more files, but the transfer rate has dropped from a good +-1000 KBs to +- 150KBs. What the.. ?
posted by elpapacito to computers & internet (5 comments total)

Sounds like your card is flawed or has reached it's read/write limit. Flash is not limitless like (theoretically) RAM/magnetic hard drives.

The OS may be decreasing the transfer rate to manage error handling. Get a new card.
posted by unixrat at 10:17 AM on May 14, 2007

it's brand new and as we speak I tried to copy again and reached 1400KBs ...it's "a mistery"
posted by elpapacito at 11:20 AM on May 14, 2007

A lot of this depends on the file system and such in use on the card, but it comes down to the fact that only a certain number of entries are allowed within the root directory. Another shining example of this can be seen by IOMEGA ZIP disks. I think their limit was 512 files or something like that, but there is no limit on the number of files in a subdirectory. There are lots of pages still out on the net explaining how to overcome this problem on zip disks.

And you found out just how to do it. Create a directory and put everything in there.
posted by chrisroberts at 12:01 PM on May 14, 2007

i didn't remember about any limit in root..anyway it seems plausible given the zip behavior. Thanks for help
posted by elpapacito at 12:13 PM on May 14, 2007

The card is probably formatted as FAT16. From Wikipedia:

The number of root directory entries available is set at formatting time, the number is stored in a 16 bit signed field setting an absolute limit of 32767 entries (32736, a multiple of 32, in practice). For historical reasons, FAT12 and FAT16 media generally use 512 root directory entries on non-floppy media, and other sizes may be incompatible with some software or devices (entries being file and/or folder names in the old 8.3 format).[2] Some third party tools like mkdosfs allow the user to set this parameter.

Source: http://en.wikipedia.org/wiki/File_Allocation_Table

Maybe the card is formatted with a very low maximum number of root directory entries? Anyway, I think issues like this are one of the reasons why most digital cameras store their files in folders rather than dumping them on the root level of the storage card -- due to the design of FAT, odd things can happen when you do.
posted by Kadin2048 at 2:18 PM on May 14, 2007