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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