Re: Battery Drain on Canon EOS Digital Rebel

From: Pierre Vandevenne (pierre_at_datarescue.com)
Date: 01/19/05 

Date: Wed, 19 Jan 2005 14:53:44 +0000 (UTC)

Chris L Peterson <clp@alumni.caltech.edu> wrote in
news:v02su01tiv9v7jtbo91efv4kcl29gqk8ge@4ax.com:

> Normally, deleting files under the FAT file system (which is what the
> Canon uses) doesn't remove the data, just the directory entry. But I
> expect that in this case the data is really gone. Writing flash cells
> requires that they be erased, which is a long operation. Better to do
> it when deleting images than doubling the write time (that is, an
> erase followed by a write) after taking the picture.

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. 

-- 
Pierre Vandevenne - DataRescue sa/nv - www.datarescue.com
The IDA Pro Disassembler & Debugger - world leader in hostile code analysis
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