questions about flash memory....

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During the last year or so, I've been watching the price of flash memory
drop, to the point where it is cheap enough to be considered as a possible
"archival" storage medium. That brings up a number of questions:

1. Aside from the obvious physical packaging, is there any significant
advantage or disadvange to choosing a memory stick, SD card, or CompactFlash
card? That is, are any of them longer-lasting, or are they all about the
same, just flash memory chips in a package?

2. Are they affected by magnetic fields? I'm not thinking about high-powered
super-conducting magnets from the supercollider, but just the type of
magnets you might find around the house.

3. Are they likely to be damaged/erased by exposure to moderate heat, such
as the interior of a car in the summer? Or intense cold, as in a Minnesota

4. While they are not generally waterproof, can they recover from an
accidental dunking in fresh water, if given time to dry out thoroughly
before being used? Or would the water short out something and cause the data
to be lost?

5. How long will the data persist? Years? Decades? Will it last longer if
each device gets plugged into a computer occasionally, or does reading them
make no difference to persistance?

6. Are they affected by airport x-ray scanners? For that matter, are ANY of
our electronic devices (PDAs, cellphones, laptop computers, digital cameras,
MP3 players, etc.) affected by being x-rayed at the airport? If so, is there
any way to prevent or circumvent this, without being labeled a terrorist???

Re: questions about flash memory....

On Fri, 15 Jun 2007 20:07:53 -0500, "Perry Noid"

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Memory stick is a disadvantage because proprietary, should
have higher cost and lower support over the long term.
Supposedly the pin-interface of Compact Flash is more
durable over time, but I doubt you'd be inserting/removing
it that many times over a few years.  Once a day is not
enough to wear any of them out.

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No, but  IIRC there is the hypothetical chance your
supercollider could do some damage.  Beyond hypothetical, I
vaguely recall people subjecting cards to strong magnets (AC
powered floppy disk eraser for example) without any effect
on them or the stored data.

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No, but some packaging/case/shell/etc plastic might be.  If
this is supposed important "archival" backup why would you
leave it in temp extremes?  

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Actually they are generally waterproof, you just have to let
it dry out completely (inside) before applying power again.

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No, nothing can be shorted out to cause a loss when power is
not applied.  However, "power" could mean a static discharge
in some environments instead of being powered by the
computer/reader device, whether it is wet or not.

They can be dunked in extremely UNfresh water, including
coffee, your washing machine, anywhere that the water does
not have substantial corrosive properties per the term of
submersion.  If the residue remaining after the card dried
were conductive, it would be important to first rinse out
the card.  If it were not (most liquids in a non-industrial
setting are not going to be a problem)  you just have to let
it dry completely and that the interface contacts don't have
residue interfering with a good connection.

In other words, they are extremely robust for all practical
purposes.  If there were a realistic chance yours would get
wet, it might be more reasonable to get a type that can be
dried out by removing the shell (USB type with a
snap-together shell opposed to glued or melted together)
instead of a card you can't open without destroying the
shell.  However, if you had destroyed the shell on (for
example) an SD card, or had to pry off the metal sides on a
Compact Flash card (and you did so carefully so as to not
damage it), you could then still get the data off after it
had dried, but it would no longer seem a reasonable method
of making backups since it would then be a nude circuit
board (though with either types, you might be able to use
filler like epoxy or caulking/etc to fill the card making it
impossible for any water to get inside, and if the sides of
a CF card aren't terribly bent up you can put them back on.
There are also some cards that claim they're waterproof but
I don't recall the brands/models, nor do I know how reliable
their claim (suppose for example a card were flexed a little
while submersed, depending on their waterproofing method it
might leak and then the waterproofing method is an impedance
to it drying out, trapping the liquid inside unless it is
physically opened to dry it).

Since practically everything electronic you own will not
like being powered while wet, it seems to mostly be a
non-issue unless you live in a flood-prone area, in which
case I suggest you get a small waterproof plastic container
to store them.

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Many claim 10 years.  Reading should not effect this, and
it's 10 years from written, not 10 years total viability
(you could refresh the data by writing it again).
Plugging and unplugging does not matter, unless you were
doing it every other minute onto the point that it
physically wore out the contacts on the card-reader
interface.  As for decades, a lot can happen in decades.
Exposure to acrid air/moisture, environmental pollution,
breakdown of a poor epoxy used to encapsulate chips,
delamination of a PCB or it's coating holding chips, etc,
etc.  I would assume (unless it's defective or alarmingly
cheap corner-cutting design) at least 30 years if stored
well (moderate temp (not an uncontrolled environment, low

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Sandisk, one of the majors has conducted X-ray tests that
show no damage.

Re: questions about flash memory....

Excellent reply! Thanks for the information... it pretty well matches what I
would have expected, but always good to get a reinforcing opinion!...

The use of "archive" was probably an overstatement... I would never rely on
storing any valuable/important information in only one place, be it a CD,
DVD, flash memory, or hard drive. Usually, I keep things in at least 2
different locations, and often on different media. I was thinking more along
the lines of accidentally leaving a flash memory device in a hot car for a
day, or forgetting to remove it from a pocket before washing clothes.

Again, thanks for a well thought-out reply!....

Re: questions about flash memory....

On Sat, 16 Jun 2007 09:40:57 -0500, "Perry Noid"

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The greatest jeopary to flash media is corruption by the OS
or device, like removing a drive improperly (writes still
cached).   This isn't a frequent occurance, but on the other
hand I had it happen just the other day after I'd ejected
media it complained and sure enough scanning it found about
2 dozen lost files.  Perhaps I should have waited longer
after ejecting it, but I didn't...

For this reason I would not have a flash card
/thumbdrive/etc as the only source of the data but rather a
redundant source, since it's highly unlikely that something
would destroy both copies simultaneously.

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