Ron Goodenow <
[email protected]> wrote:
Just curious to know where you got the lifespan data. I've got el-cheapo
data and audio discs (both cdr and cdrw) burned over five years ago that
are reading perfectly and, having read tons of stuff on cdr's have never
seen such a short span projection. With the costs of today's blanks I do
tend to back up discs from that far back but only to be doubly safe. Thanks.
That was exam material that I took on Tuesday in an Architecture
class. The book did not state the lifespan. The instructor did as we
discussed it.
Note: CD-RW is a totally different approach than CD-R.
The dye layer in CD-R's evidently is not stable over time. Or, that is
the only conclusion that I can draw from the information. The book
does not address this issue, but that looks like a logical deduction.
My CD-R was written and stored immediately in a hard jewel case in a
dark drawer. After 3 years the writer could not read the CD, although
my DVD did. That was the second time it had been removed from the
case.
You might be safer in your CD-RW's. Nothing about a lifespan was
mentioned about these, other than for overusage.
<q>
The CD-RW optical disk can be repeatedly written and overwritten, as
with a magnetic disk. Although a number of approaches have been tried,
the only pure optical approach that has proved attractive is called
phase change. The phase change disk uses materialthat has two
significantly different reflectivities in two different phase states.
There is an amorphous state, in which the molecules exhibit a random
orientation and which reflects light poorly; and a crystalline state,
which has a smooth surface that reflects light well. A beam of laser
light can change the material from one phase to another. The primary
disadvantage of phase change optical disks is that the material
eventually and permanently loses its desirable properties. Current
materials can be used for between 500,000 and 1,000,000 erase cycles.
A key advantage of the optical disk is that the engineering tolerances
for optical disks are much less severe than for high-capacity magnetic
disks. Thus, they exhibit higher reliability and longer life. </q>
This sounds far better than CD-R and they don't cost all that much
more. They can be reused to boot.
Back to CD-R, each block is 2352 bytes. The last 288 bytes are error
correction code. If you verify the write each block should contain an
error correction code for the block. But, back to the drawing board...
if your CD writer cannot read the CD after a period of time, what good
is the error correction code?
If you don't verify the write you get an extra 288 bytes per block to
store data on.
I think CD-RW sounds like the better choice, until we can afford DVD
writers at least.
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