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Re: JFFS2 (not) on CF cards

On Sat, 09 Mar 2002 05:58, Alan Cox wrote:
> > > How do non-Linux systems handle this (i.e., my camera, windows, mp3
> > > players, etc...) -- I believe they use fat32 or some nonsense, right?
> > > Same problems?
> >
> > yes, yes.
> CF cards do wear levelling on card (or are supposed to anyway). Most
> cameras seem to use FAT12/FAT16

Well not really.... We've pounded this to death a few times already.

Internally CF does something like what SmartMedia block drivers do; when they 
allocate new blocks for the physical to logical virtualisation layer they do 
this off a pool. ie
When a sector is rewritten, a new block is grabbed from the pool and 
unmodified sectors are copied across. The old block is erased released back 
into the pool.

This semi-random reuse effects a limited form of wear levelling. This is not 
"counted wear levelling". This kind of wear levelling does not prevent or 
correct for seldom-changed files "squatting" on an area of flash and 
preventing this area from being levelled.

IMHO CF is a Kleenex technology. While you can use CF in an embedded system, 
it is prone to failure and can thus cause product failure. Rather only use CF 
as a removeable data transfer (as it was designed for). 

FAT16 seems to be the most popular. Of course if you need to interchange data 
with cameras, PCs etc, then you don't have too much choice.

-- Charles

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