> --Do we know how long this medium of storage is reliable,
> compared to, say, DVD?
Nobody knows for sure. The longevity of various storage media is just
an estimate based on some tests. But the DVD medium is thought to
have a longevity of 25 to 100 years, depending on the composition of
the DVD and the conditions under which it is stored. Data on flash
memory is believed to be good for 10 years. If the data is refreshed
(copied from and then back onto the flash memory) then it's good for
another 10 years.
> --What is the significance of the "speed" that the CF cards claim?
The speed rating is supposed to tell you the capability of the card to
read and write a sustained stream of data. Compactflash was first to
offer ratings. The manufacturers stated the speed as multiples of X,
where X= 150,000 bytes per second. So a card rated at 10X would have
a sustained write speed of (150,000 * 10) = 1.5 million bytes per second.
For digital audio recording, a sampling rate of 24/96 generates a data
stream of 576,000 bytes per second, so theoretically a Compactflash
card rated for 4X speed would be sufficient. In practical terms,
there are no Compactflash cards rated much slower than 40X, so just
about any Compactflash card should be OK for use in a digital recorder.
A new "Class" speed rating system was introduced with SDHC cards.
Class 2 has sustained write speed of 2 million bytes per second, Class
4 = 4 MB, and so on. The higher speeds are necessary for recording
digital video. For example, AVCHD encoding used by Sony and Canon in
some of their new models creates a data stream up to 3 MB per second
of audio and video information.
"Class 2" (2MB per second) is equivalent to 13X in the old system.
"Class 4" (4 MB per second) = 26X
"Class 6" (6 MB per second) = 40X
In practical terms, there are no "Class 1" cards. A "Class 2" card is
fast enough for 24/192 audio recording.
Unfortunately, some recorders have trouble with flash cards
manufactured by particular vendors. The Tapers Section web site has a
forum where the topic, "Which cards work with which recorder," is
discussed.
http://taperssection.com/index.php/topic,97893.0.html
--oryoki
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