Roger,

I don't have any problems with what you wrote.  There are perhaps a couple
of points I didn't raise:

- while I agree that the OS will not overwrite the space occupied by
deleted data, it does need to keep a pointer to that "free but used"
space, so that when adding a file it doesn't re-use the "deleted" file's
disk space.  We know that DOS does this when it can, but I don't know
about camera firmware.  From one experience, I suspect at least the Nikon
5700 does.

- one should try and keep the number of writes to a CF to the minimum.
Does deleting a thousand pictures or reformatting the card result in fewer
writes?

D200 - get a magazine to commission something, or review the camera?

73,
David

<snip>

Summarizing after reading the posts in this thread, there seem to still
be some misunderstandings about formatting versus deleting solid-state
memory cards, so here is my understanding of what happens with the
various methods.

Formatting a card in the camera does not do anything at all with the
images that are stored on the card.  Formatting in-camera simply
rewrites a new FAT(32) table, and creates the directory structure
required by the camera.  A file recovery program can still recover all
the images on the card, providing of course they are not corrupted by a
malfunctioning card or camera.

Deleting images simply marks the FAT entry and frees the memory space
used for the deleted file(s), for use by subequent images which will
overwite the older image.  The images are still on the card, and can be
recovered as above.  The disadvantages with deleting are that you may
have a corrupted FAT table, locking out sections of the memory, and it
takes longer to delete all the FAT entries since they are done one at a
time.  Reformatting achieves exactly the same result, by simply writing
a new FAT table, and in my opinion is the preferable option.  This also
applies to 'moving' files when uploading to the computer.  The moving
procedure copies the file and then deletes it from the card by marking
the FAT entry as above.  The images are still there as before.

Roger is mistaken when he mentions above that it could take up to 10
cycles to wipe a card.  That is the case with magnetic storage as in
hard drives because of residual magnetized 'fringes' left at the side of
the tracks, because the read/write head doesn't track in exactly the
same place each time, due to mechanical tolerances, temperature, etc.
With memory cards, though, when a bit assumes a 1 or 0 state from being
written to, there is no trace left at all of any earlier state that bit
may have held, so multiple wipes are unnecessary, and achieve nothing.  
The only way to ensure there is no image left on the card is to use a
program that writes some pattern or other of ones and zeroes to the
entire card, and it needs to do it only once.  Some secure programs look
at a file to determine its length, and then overwrite the file with
random 'data', but these programs are slowish since they deal file by
file.  A global write is much quicker.  This is the only way to really
clean a card, since neither formatting nor deleting removes images from
the card.

Colin D.