Re: Reformat Sd-Card?

Get some better engineers.

Agreed :)

An SD card's memory has a limited number of times that it can be used and
rewritten. To get around this limitation the card uses different areas of
its memory at different times, greatly extending the life of the memory
cycles to the point that it is quite practical. But it is not always a
contigous block.

That's not really correct. There is no such 'magic' in the flash controller.
It just makes sure it maps out the useless bits (in general, in 4-8 bytes at
once); still, the operating over the microcontroller system doesn't see
anything of this. That is, logically, this results in no additional
fragmentation resulting in the need of, for example, adding new FAT
entries - logically.

BTW, even EEPROM's have a very good life expectancy. The next excerpt (p.77)
is from the "Smart Card Handbook" from John Wiley and Sons, one of my
favouite Smart Card handbook:

"EEPROM is one of the few types of semiconductor memory having a limited
number of
access cycles. It can be read any number of times, but it can be programmed
only a limited

number of times. The reason for this limitation can be found in its
semiconductor structure.

The life expectancy of an EEPROM depends strongly on the nature, thickness
and quality

of the tunnel-oxide layer between the floating gate and the substrate. Since
this layer must

be produced very early in the fabrication process, it is exposed to strong
thermal stresses in

subsequent fabrication steps. This may cause damage to the oxide layer,
which in turn affects

the useful life of the EEPROM cell. During fabrication, and every time the
cell is written,

the tunnel-oxide layer absorbs electrons that are not subsequently released.
These 'trapped'

electrons are located close to the channel between the source and the drain,
and once they

reach a certain number they have a stronger effect on the threshold
potential than the charge

stored in the floating gate. When this happens, the EEPROM cell has reached
the end of its

useful life. Although it can still be written, the charge on the floating
gate has only a minimal

effect on the characteristics of the channel between the source and the
drain, so the threshold

potential always remains the same. The number of possible write/erase cycles
varies greatly,

depending on structural details. Typical values range from 100,000 to
1,000,000 cycles over the

entire range of operating temperature and voltage. At room temperature and
using an optimum

supply voltage, values that are 10 to 50 times greater can be achieved.

When an EEPROM cell is approaching the end of its life, its data retention
time decreases.

The retention time can range from hours to minutes or even seconds. The more
exhausted the

EEPROM becomes, i.e., the more electrons that have been absorbed by the
tunnel oxide layer,

the shorter is the retention time."





As for defragging a SD card, that is not required, nor would I recommend
it.

Nor would I. Simply moving the files off the card (and probably formatting -
but that's, in general, not needed) and, then, moving the files back to the
card will suffice. Again, I recommend my articles on this subject - I've
explained all this stuff in depth there.

After all, the card is managing itself quite well, and rearranging the
memory locations used will probalby not result in a contigous block in any
means - that is, if the card is doing as it is supposed to and utilizyzing
all available memory location evenly.

Again - this is at the physical level, not at the OS level. The
microcontroller does rearrange SOME stuff (when some cells become dead), but
the OS doesn't see anything of this. Furthermore, the microcontroller does
NOT arrange fragmented files to be unfragmented - its only task is,
rearrangement-wise, is mapping out the bad bits. That is, there *will* be
fragmentation.


BTW, I've done quite a lot of work with SmartCards (even programmed them).

--
Werner Ruotsalainen - Microsoft MVP - Windows - Mobile Devices
Please see my blog at http://www.pocketpcmag.com/blogs/index.php?blog=3 -
you will definitely like it.


"xTenn" <xTennRemoveThisPart@xxxxxxx> wrote in message
news:O$Ut1OTTGHA.196@xxxxxxxxxxxxxxxxxxxxxxx

"Dr. O'Woodard" <DrWoodardOnDS@xxxxxxxxxxx> wrote in message
news:kis022lnrp528a8pa84ktb7mi6jp712h6o@xxxxxxxxxx
On Tue, 21 Mar 2006 13:01:27 -0600, "Clinton Fitch {MVP-Mobile
Devices}" <management@xxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:

I disagree.

Just because it is solid state does not mean that it does not fragment.
Fragmentation has more to do with the OS than the physical platform.

Regards,
The engineers tell me the files can't be fragmented. That every time
you save to a solid state card like SD the the entire contents of
every file is re-written to the card in contigous form. This from
engineers I know who worked at HP.


Get some better engineers. An SD card's memory has a limited number of
times that it can be used and rewritten. To get around this limitation
the card uses different areas of its memory at different times, greatly
extending the life of the memory cycles to the point that it is quite
practical. But it is not always a contigous block.

As for defragging a SD card, that is not required, nor would I recommend
it. After all, the card is managing itself quite well, and rearranging the
memory locations used will probalby not result in a contigous block in any
means - that is, if the card is doing as it is supposed to and utilizyzing
all available memory location evenly.





.

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