One would hope that the Sandisk WORM SD cards which they claim a life of 10=
0 years for. Do actually last that long?
Phil
On 27 Jun 2010, at 01:33, Jeremiah Moore <> wrote:
I had a long talk with an engineer friend who works in flash memory. It wa=
s
geeky but illuminating.
Each flash memory cell is a small capacitor. One interesting fact is that
in order to read it, the bit must be actively flipped. And reading disrupt=
s
other cells in the same column. In fact, in the process of reading, the
memory is re-written. Cells have a lifespan and begin to degrade after a
certain number of cycles. There is a considerably large amount of error
going on almost all the time, but it's a generally predictable degree and
type of error, so data is written with a degree of redundancy using error
correcting read/write algorithms. A microcontroller keeps track of which
cells or areas are experiencing higher degrees of error and as they begin t=
o
fail they are permanently blocked out.
Personally, I trust flash memory long-term about as much as any other
medium, which is to say I have reservations. I believe the only best
practice involves redundant copies stored in disparate locations, and
periodic verification and re-copying.
-jeremiah
On Sat, Jun 26, 2010 at 3:57 PM, Mitch Hill <> wrote:
At 10:35 PM 6/26/2010 +0000, you wrote:
it is
still possible for any given specimen to fail within the first hour
of use. It's just statistically less likely.
Like a light bulb, most failures seen to happen during a transition such
as from unpowered to powered.
I seem to remember some years ago a company was developing a way to
preserve data onto paper. I believe they were able to transcribe the 1's &
0's to print on archival paper. And a way to accurately scan that back
into digital.
Actually, keeping data on paper for archival purposes has been around for a
long time. And I'm not talking about the bible...
Way back, in 1958-59 that I know of first hand, my father in his business
used punched digital paper tapes and punch cards for data storage and
retrieval. A duplicate set was maintained in a bank vault in town and
weekly, updates were made and swapped with the ones in the vault. I
believe this method dates back into the late 1940's, was very labor
intensive and costly and we've come a long ways since then...
But I can still hear the chatter of the mechanical Frieden (sp?) tape punch
chugging along to this day...
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