An interesting read. I'd like to have had this article available about
three years ago if I also could have gotten the requisite data from the
manufacturers.
At the company I last worked for we built some navigational display
screens for the navy. They had an on-board processor running Windows NT
to handle the computations and graphical display. Storage was on a 10GB
notebook drive.
The navy liked them and came back for more. Since we could no longer
get the same flat panel display we had used previously we had to do some
re-engineering of the case. Since the display also had to be hardened
against explosive shock we decided to try substituting CF cards for the
hard drives figuring they would be more reliable in battle conditions.
Surprisingly, it's possible to fit a stripped down verison of Win NT on
a 384MB card.
We were aware of the 100,000 write cycle limitation of the CF cards so
we decided to side step the issue completely. We upped the DRAM memory
requirement to assure that the OS would never have to use the CF card as
swap space. Since there were no other applications installed or running
other than our own custom navigational display (which wrote nothing to
files) we concluded that writes to the CF card should be practically
non-existent.
Much to our surprise we discovered about a 5% failure rate on the CF
cards during the first year. When the navy came back for more displays
we built the next set using a different brand of CF card. Last I knew
those seemed to be heading for a similar failure rate. Since the CF
card was still the right solution for explosive shock the decision was
to stay with it and the set after that was redesigned to make it much
easier to get into the case and change the CF card with a spare.
Why the failures? We never knew but it certainly wasn't from doing too
many writes. Maybe CF cards aren't really designed to be powered on
24/7. But they're much better performers in the explosive shock test.
(You mount your equipment on a test stand on a small barge. Then a 60
pound dynamite charge is set off right next to the barge. Your
equipment has to stay running throughout)
Chuck Norcutt
Tim Hughes wrote:
> For hard core technochrats, here is an inside design view of flash
> memory cards etc.
>
> Different technologies and reliabilities for different markets. How
> they achieve reliability using error correcting ("Reed-Solomon
> codes") and block replacement, load leveling etc. There is a lot more
> to this than you think. Unfortunately it does not help you much in
> choosing a CF card say, as you would need to pry this from the
> vendors spec sheets and they likely don't publicise it to consumers!
>
> http://www.edn.com/article/CA6298274.html?nid=2431&rid=2026776195
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