Dunno where you heard this. Sounds like web lore to me.
From the Wiki article on flash memory
<http://en.wikipedia.org/wiki/Flash_memory>
NAND devices also require bad block management by the device driver
software, or by a separate controller chip. SD cards, for example,
include controller circuitry to perform bad block management and wear
leveling. When a logical block is accessed by high-level software, it is
mapped to a physical block by the device driver or controller. A number
of blocks on the flash chip may be set aside for storing mapping tables
to deal with bad blocks, or the system may simply check each block at
power-up to create a bad block map in RAM. The overall memory capacity
gradually shrinks as more blocks are marked as bad.
NAND relies on ECC to compensate for bits that may spontaneously fail
during normal device operation. A typical ECC will correct a one-bit
error in each 2048 bits (256 bytes) using 22 bits of ECC code, or a
one-bit error in each 4096 bits (512 bytes) using 24 bits of ECC
code.[22] If the ECC cannot correct the error during read, it may still
detect the error. When doing erase or program operations, the device can
detect blocks that fail to program or erase and mark them bad. The data
is then written to a different, good block, and the bad block map is
updated.
Dr. (wear leveled and bad block managed) Flash
On 3/23/2013 2:26 AM, Ian Manners wrote:
> SD cards don't have on board controllers.
> CF cards have on board controllers.
>
> I prefer CF cards but SD cards are cheaper and
> still have there place, called space :)
>
> What I tell everyone to do, doesn't matter what type of card
> they use, remove all images from your card occasionally,
> if your only an occasional camera user then mark on your
> calendar to reformat your camera card at the same time
> you change your smoke detector battery. Ya, like they
> will remember but at least I've told them.
>
> If your a bit more anal, reformat your card every ten times
> after you have erased all files (obviously after downloading
> them somewhere else). Especially SD cards, they are also
> cheap enough that you can replace them at some point
> especially if you are a heavy user.
>
> I do it whenever, I kind of know I copied off a few times
> and deleted files so I'll reformat instead of simply deleting
> whenever.
>
> Why delete instead of formatting ?
>
> Simply deleting files means people like me can normally
> recover most if not all files in case of emergency.
>
> Formatting a card means a lot more work, and probably
> files damaged/not recovered properly.
>
> You can only write to static memory so many times
> until damage occurs that cant be repaired. When damage
> occurs in the data area, the file system can map the
> damage out in the file index.
>
> With FAT the file index is normally in one part of the 'disk'
> and isn't movable, formatting a card/disk, you are slightly
> increasing the chance that an error/damage will occur to
> the file index table.
>
> Simply deleting the files minimises the risk of damage to
> the file allocation table's.
>
> Simply deleting files on a memory card leads to fragmentation,
> and depending on usage my friends and relatives will eventually
> call me with weird problems, like being able to view photos on
> the camera but cant copy them off, or photos are corrupt or
> something else. At some point a card should be reformatted
> to reinitialise the file tables and to lay down the file markers
> on the 'disk'. reinitialising the tables means the first time
> you use the card there shouldn't be any fragmentation.
>
> Memory cards do over time lose bit's, especially if subject to
> some types of radiation, heat, and even motion due to conversion
> of kinetic energy. The damage is cumulative, if you go through
> an airport scanner it might take 50-100 trips before a problem
> occurs, a lot better than film, most times normal error correction
> will get around corrupt bits and file the gaps left but if the actual
> file allocation table is damaged, this is were it can get difficult.
>
> It's a numbers game, some people never reformat a card until
> the day they throw the PnS camera out, some people never
> delete photos, they simply put a new card in when they have
> filled the first card. The old card then goes into storage in a
> plastic box under the microwave or near the heater..
>
> It's all about minimising the chance that you will have a problem.
>
> And some cards are just sh1t.
>
> Cheers
> Ian Manners
> Of nowhere in particular.
>
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