RE: [DML] CD-Rs, CD-RWs

["Wright, Ryan (LW)" <Ryan.Wright@xxxx>]

Moderator's note: I agree with Ryan's first statement here. While many of us have an interest in this subject I think it's been pretty well covered at this point so I think I'll kill it after this statement.
Bruce, this week's moderator]


We've really beat this off topic subject to death, so this will be my last
(public) post on it:

You're mostly right, George/Farrar (both names are listed on your reply, so
I'm not sure which one to use! :) ).

>> CD-Rs are manufactured by burning holes in the silver

Actually, the laser burns pits into the media, not holes (also, the media is
not silver, it is a chemical dye mixture, though it may contain trace
amounts of silver). Incidentally, CDRs are also not "encased" in plastic.
There is a plastic disc with a layer of dye on top of it. The top of the CD
- the "label" that you write on - IS the media, though it's a common
misconception that there is plastic both on the top and the bottom with
media sandwiched in the middle. People try not to touch the "surface"
(bottom) of the disc, when in reality the top is much more sensitive. (but
you already pointed this out!)

Like you said, if you scratch the top of a CDR, you will take the media
right off the disc. I've got some discs that are completely clear because
the dye wasn't applied correctly and it flaked off after only a few hours of
use. It's real bad when you get it in your CD player, because it can destroy
the drive. (we lost a CDRW drive that way)

>> CD-RWs, on the other hand, don't actually burn the layer
>> of silver. They burn another layer (this is where my memory gets fuzzy
>> - can't remember if it's plastic or silver), which cannot be seen by
>> consumer-grade players. 

CD-RWs do not burn a layer, they change the status of the layer. Think of a
liquid crystal display. Electricity is applied to a single pixel, and it
lights up. Remove the power and it goes blank. Well, with a CDRW, the laser
uses heat to change the surface of the disc to be either a pit or the lack
of a pit. The status of each "sector" on the disc can be changed a couple
thousand times, thus the rewritable capability. This works well, but the
material used to accomplish this on the disc itself is less than half as
reflective as a standard CDR. As a result, the laser needs to operate at a
much higher power level in order to reflect enough information back to read
the disc. When you put a normal CDR in the drive, the laser drops it's power
level back to normal.

Very few (>5%) audio CD players have the capability to adjust the power on
their laser, and as a result, cannot read the less reflective CDRW discs.
Incidentally, almost all CD-ROM drives nowdays do have this capability.
Older drives (older meaning a couple of years ago) usually cannot read
CDRWs. I've got some drives that can, and others that can't.

One of the reasons CDRWs are heavier than CDRs is they actually do have two
layers of plastic with the media sandwiched in between. If you compare them
to a standard CDR, you'll notice they are slightly thicker. Also, the
chemical within the disc is not only heavier, there's more of it.

>> For those consumer-grade recorders, you have to get "music only" 
>> discs, which will play in just about anything.

The "music only" discs are actually no different in media than regular CDRs.
They are a ploy by the recording studios to deter piracy. When standalone CD
recorders became available, it made CD recording available to everyone else,
when up until then it had been mainly for computer geeks like myself. The
RIAA freaked out and demanded a scheme to reimburse them for "lost sales",
as they assumed the devices would be used for piracy. Standalone CD
recorders have the capability to record to any regular old CDR, but due to
these RIAA imposed regulations, they first check the disc for a code to see
if it's a "music" disc. These "music" discs are encoded with data that tells
the standalone recorder it's OK to record to them. They cost five times as
much and all of that extra money goes to the RIAA.

In effect, they're assuming you're going to pirate music with the devices
and charging you a premium for the discs to recoup some of their costs. It's
bulls---, but the only thing you can do about it is not buy a standalone CD
burner.

Incidentally, you can buy the overpriced "music only" discs and record audio
and/or data to them with a computer and they'll work just fine. They won't,
however, work any better than a cheaper CDR, because they're made of the
same materials. Like I said, the extra cost is not for a superior disc, it's
a premium paid to the recording industry.

Hope this helps.

- Ryan Wright, MCP (ryan.wright@xxxx)
- Web Operations Analyst
- Lamb-Weston, Inc.

-----Original Message-----
From: George Liquor [mailto:smeghead79@xxxx]
Sent: Thursday, March 29, 2001 1:12 AM
To: dmcnews@xxxxxxxxxxxxxxx
Subject: [DML] CD-Rs, CD-RWs

[disengage lurk mode]

Hi, all!

Somebody earlier reported that there's no standard for CD-RWs and that's
why they can't be played in consumer-grade players. This is not true.