Digital BW, The Print

On 16 Sep 2004 at 17:34, Avery Minor wrote:

> This is my theory of how this happens to memory cards:  When the write to
> card is interrupted for any reason, an incomplete image/file is created.
> This file doesn't have the proper end of file or some other significant
> code. An attempt to read, write or format the card becomes impossible by
> resulting in an infinite attempt to read.
> 

I don't think it's that complicated, digital cameras use the FAT file system, named 
after the File Attribute Table.  It really means Freakin' Absolutely Terrible file 
system, what it does, is at the end of each block of data, it puts a Cylinder-Head-
Sector pointer to the next block.  Take a 256MB card, it appears to have 64 sectors 
per head, one head, and 4096 cylinders, each sector being 1024 bytes long.  

So it's reading a long, and the next pointer states cylinder 7254, the software 
doesn't know what to make of this, so it, states that the card has a problem.  Which 
it does, the cylinder number isn't in the normal range of numbers.  Reformatting 
simply states that the media is empty, because it's not really a disk, it's a block of 
memory.    This is actually preferable to if every camera maker designed their own 
memory access scheme.  

> I use a program which I downloaded for free to recover lost images. When the
> images are read there is usually one which is truncated, but the recovery
> program gives it the necessary coding to be read.
> 

For the bext success, if you need this, always download then erase the whole card, 
because what happens then it that each photo will cover sequential sectors, so the 
recovery software can simply sequentially read the card, throw away the CHS 
pointers, and read block after block, into the same file, until it sees another image 
JPEG or RAW header, which it will take as the beginning of the next photo.

W