Media Longitevity/Care

Eric Smith eric at
Wed Mar 16 19:43:11 CST 2005

Guy wrote:
> It doesn't
> require *any* lab environment (just the right software and suitably
> compliant a CDwriter that allows "raw" writes).

I was assuming a "normal" CD-writer, which can't be assumed to
support raw writes.  Many CD-writers don't, and some that do claim
to support raw writes do so incorrectly.

If you can do raw writes, you can guarantee the alignment of the
"data" to the subcode framing.  Otherwise (with a non-raw-write-capable
drive, you cannot, and thus you can't predict the complete details
of the actual EFM sequence that will be written to disc.  Though to
be fair, that only will affect 14 channel code bits out of every 1372.

But even after you've done all that, you're not going to find a way to
generate any channel data pattern that is significantly more succeptible
to externally induced error (e.g., oxidation) than what you will get
from random data.  That was my original point.

> I've done this work.


I hacked my own software to read a CD based on raw preamp output, in
order to investigate copy-protected discs, but what would the point
be in developing anything that could generated a desired EFM channel
pattern from application-level data, unless you were developing or
validating a CD writer?


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