Re: Battery Drain on Canon EOS Digital Rebel

From: Chris L Peterson (clp_at_alumni.caltech.edu)
Date: 01/19/05 

Date: Wed, 19 Jan 2005 16:15:40 GMT

On Wed, 19 Jan 2005 14:53:44 +0000 (UTC), Pierre Vandevenne
<pierre@datarescue.com> wrote:

>In general, and as far as Canon is concerned, you are roughly right. The
>digital camera world is full of surprises though and both Fuji and Olympus
>cameras using smartmedia and XD cards perform full cards "true erases" in a
>matter of seconds. A format or a problem in a Canon camera is almost always
>recoverable.
>
>As you righly point out, actually writing to a card takes time. So how do
>Olympus and Fuji perform true erases? They exploit an added level of
>indirection between the flash memory and the apparent file system to zero
>the pointer table. That is unrecoverable with conventional card readers.
>
>Erase followed by writes aren't used anymore I believe.

Interesting. I use conventional flash memory all the time, and it all seems to
require an erase cycle before a write. But unlike CF, it also doesn't support
single cell erase/write cycles, but is sectored. It seems pretty obvious that CF
allows single cells to be reused, so the memory architecture is quite different.

Of course, recovering files from CF after some sort of corruption, especially in
the directory, might be completely different than recovering files that have
been erased. One thing I have noted with the 300D is that erasing a single image
takes a long time (which seems suggestive of erasing the actual cells and not
just modifying a table entry). I normally don't erase the card after downloading
images, but rather I format it. That can be done much faster- a fact that I have
attributed to the use of block erasure, a mode supported by conventional flash
where many cells are cleared at once. But if a block erase is being used, the
images would be unrecoverable after a format, which (if I understand you
correctly) isn't the case. So I wonder why erasing an image takes so long. Maybe
the camera performs some sort of defrag when erasing a single image?

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

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