"Write-once media is manufactured similarly to conventional playback-only discs. As with regular CDs, they employ a polycarbonate substrate,

 a reflective layer, and a protective top layer. Sandwiched between the substrate and reflective layer, however, is a recording layer composed

of an organic dye. .... Unlike regular CDs, a pre-grooved spiral track is used to guide the recording laser along the spiral track; this greatly

simplifies recorder hardware design and ensures disc compatibility."

Your basic CD-R is layered like this, from top to bottom:

[optional] label
[optional] scratch-resistant and/or printable coating
UV-cured lacquer
Reflective layer (24K gold or a silver alloy)
Organic polymer dye
Polycarbonate substrate (the clear plastic part)
 

Yes, it's real gold in "green" and "gold" CDs, but if you hold a CD-R up to a light source you'll notice that it's thin enough to see through (the

gold layer is between 50 and 100nm thick). Something to bear in mind is that the data is closest to the label side of the CD, not the clear

plastic side that the data is read from. If the CD-R doesn't have a hard top coating such as Kodak's "Infoguard", it's fairly easy to scratch

the top surface and render the CD-R unusable.

A pressed CD has raised and lowered areas, referred to as "lands" and "pits", respectively. A laser in the CD recorder creates marks in the disc's

 dye layer that have the same reflective properties. The pattern of pits and lands on the disc encodes the information and allows it to be retrieved

 on an audio or computer CD player. See section (2-43) for specifics.

Discs are written from the inside of the disc outward. On a CD-R you can verify this by looking at the disc after you've written to it. The spiral track

on a 74-minute disc makes 22,188 revolutions around the CD, with roughly 600 track revolutions per millimeter as you move outward from the

 lead-in (23mm from the center) to the outer edge at 58mm. If you "unwound" the spiral, it would be about 5700 meters (3.5 miles) long.

The construction of a CD-RW is different:

[optional] label
[optional] scratch-resistant and/or printable coating
UV-cured lacquer
Reflective layer (aluminum)
Upper dielectric layer
Recording layer (phase change film, i.e. the part that changes form)
Lower dielectric layer
Polycarbonate substrate (the clear plastic part)
 

See the net references section for pointers to more data (especially http://www.cd-info.com/). You can find some nice drawings at http://www.pctechguide.com/09cdr-rw.htm. The various pages connected to http://www.chipchapin.com/CDMedia/cdda5.php3 have some

 computations on disc parameters.

The Philips document "Principles of Phase Change Recordings" at http://www.licensing.philips.com/information/cd/rec/ has some nice

 drawings and a very detailed explanation of how CD-RW works.

Subject: [2-2] What is XA? CDPLUS? CD-i? MODE1 vs MODE2? Red/yellow/blue book?
(2002/12/20)

A quick summary of standards and commonly used identifiers:

Red Book

physical format for audio CDs (a/k/a CD-DA)

 

Yellow Book

 

physical format for data CDs

 

Green Book

 

physical format for CD-i

 

Orange Book

 

physical format for recordable CDs

Part I

CD-MO (Magneto-Optical)

 

Part II

 

CD-WO (Write-Once; includes "hybrid" spec for PhotoCD)

 

Part III

 

CD-RW (ReWritable; originally called CD-E)

 

White Book

 

format for VideoCD (often written "VCD")

 

Blue Book

 

CD Extra (occasionally used to refer to LaserDisc format)

 

CD Extra

 

a two-session CD, 1st is CD-DA, 2nd is data (a/k/a CD Plus)

 

MODE-1

 

standard 2048-byte Yellow Book sectors, with error correction

 

MODE-2

 

2336-byte sectors, usually used for CD-ROM/XA

 

CD-ROM/XA

 

eXtended Architecture; CD-ROM/XA MODE-2 defines two forms:

FORM-1

2048 bytes of data, with error correction, for data

 

FORM-2

 

2324 bytes of data, no ecc, for audio/video

 

ISO-9660

 

file layout standard (evolved from High Sierra format)

 

Rock Ridge

 

extensions allowing long filenames and UNIX-style symlinks

 

CD-RFS

 

Sony's incremental packet-writing filesystem

 

CD-UDF

 

industry-standard incremental packet-writing filesystem

 

CD-Text

 

Philips' std for encoding disc and track data on audio CDs

CD-ROM/XA is an extension to the Yellow Book Mode 2 standard. It was intended as a bridge between CD-ROM and CD-i (Green Book).

See http://www.licensing.philips.com/ if you want to buy copies of the standards. They're not cheap! You can download some of them from http://www.ecma-international.org/. ECMA-119 describes ISO-9660, and ECMA-130 sounds a lot like "yellow book" if you say it slowly.

For SVCD, see http://www.iki.fi/znark/video/svcd/overview/. The discs are a modified White Book format, using a 2x player and variable

 bit rate MPEG-2 instead of MPEG-1 at 1x like VCD.

For HDCD, see http://www.hdcd.com/. The discs are in Red Book format, but the low bit of the audio has additional information encoded in

it. They sound good on a standard CD player, and better on an HDCD player.

SACD isn't really a CD format. It can have a Red Book compliant layer that is read by standard CD players, but to get the high-fidelity benefits

you need a special player.

Subject: [2-3] How do I know what format a disc is in?
(2001/07/09)

You can usually tell by looking at the packaging and/or the disc itself:

• CD-DA discs will have a "Compact Disc Digital Audio" logo.
• CD+G discs will have the words "CD Graphics" (and perhaps even CD-EG "Extended Graphics").
• CD-i discs will have a "Compact Disc Interactive" logo.
• VideoCD discs will have a "Compact Disc Digital Video" logo and/or the words "VideoCD".
• PhotoCD discs will most likely say "Kodak PhotoCD" on them.
• SVCD discs have a "Super Video CD" logo (the words "Super Video" under the standard CD logo). The discs use one of the standard
• CD-ROM formats.
• DVCD discs say "DVCD"?? [ can't find much info about DVCD ]
• HDCD (High Definition Compatible Digital) have an "HDCD" logo. See http://www.hdcd.com/. The discs appear to use the standard
• Red Book format.
• SACD (Super Audio Compact Disc) is relatively new. The discs can have two layers, one of which is in Red Book audio format, the
•  other in a DVD-like format offering higher fidelity.
• DTS (Digital Theater Surround) CDs are just like normal CDs, but use DTS encoding instead of PCM. See (2-34).

VideoCD is different from CD-Video (a/k/a "Compact Disc Video", or CD-V). CD-V is an analog format, like LaserDisc, and the video can't be

viewed with a CD-ROM drive.

There are a few references to Compact Disc MIDI, or CD-MIDI.

See (4-46) for some comments on High Speed CD-RW.

Subject: [2-4] How does copy protection work?
(2002/04/01)

Copy protection (sometimes erroneously referred to as "copyright protection") is a feature of a product that increases the difficulty of

making an exact duplicate. The goal is not to make it impossible to copy -- generally speaking, that can't be done -- but rather to discourage

"casual copying" of software and music.

The goal is *not* to conceal information from prying eyes; see section (3-19) for information on encrypting data on a CD-ROM.

A separate but related issue is "counterfeit protection", where the publisher wants to make it easy to detect mass-produced duplicates.

An example of this is Microsoft's placement of holograms on the hubs of their CD-ROMs. There are full CD pressing plants dedicated to

creating counterfeit software (the worst offender being mainland China), so this is a serious concern for the larger software houses.

Copy protection on CD-ROMs used to be rare, but as the popularity of CD recorders grew, so did the popularity of copy protection.

A large percentage of games released in the past few years have been protected.

A more recent innovation is copy protection for audio CDs, inspired by the rise of MP3 trading over the Internet. This is more difficult to do,

because the protection must allow correct behavior on a CD player but altered playback when being read by a CD-ROM drive. The best

 that can be accomplished is to force the user to play the music in an analog format and then re-digitize it, resulting in an imperfect

reproduction.

The article at http://news.cnet.com/news/0-1005-201-7320279-0.html is a nice introduction to the issues.

Some people have questioned whether copy protection is legal. In some countries it may not be. In the USA, the law allows "fair use"

 of copyrighted material, but does not require that the content provider make it easy for you to do so. So while making a copy of a song

 for your own private use may be legal, there is nothing in the law that requires the publisher to make the material available in an

unprotected format. Copy protection has been around for many years -- some of the schemes employed on the Apple II were remarkably

elaborate -- and has never been challenged on legal principle.

See http://overclockers.com/tips907/ for an article about why "fair use" is a legal right rather than a constitutional right in the USA,

and what that means to you. The article also has some interesting quotes from the courts regarding the DMCA and DeCSS, notably this

one: "We know of no authority for the proposition that fair use, as protected by the Copyright Act, much less the Constitution, guarantees

copying by the optimum method or in the identical format of the original." In other words, arguing that "fair use" means the publisher

must allow you to make a perfect digital copy (as opposed to a lower-quality digital or analog copy) is without merit.

The next sections discuss data and audio individually.

Subject: [2-4-1] ...on a data CD-ROM?
(2002/12/09)

There are several approaches. An article with a good overview of some popular protection technologies can be found at http://www.tomshardware.com/storage/02q2/020617/index.php. Another source is the "CD Protections" articles on http://www.cdmediaworld.com/hardware/cdrom/cd_protections.shtml.

For anyone interested in protecting their own discs: don't bother. Copy protection, on the whole, does not work. If you have a major

application, such as a game or CAD package, you may want to consider one of the commercially licensed schemes listed later,

or (heaven forbid) the use of a dongle. In general, though, if the disc can be read, then the contents can be copied. If you don't want

somebody to make a copy of your stuff, then you'd better encrypt it (3-19).

A simple and commonly seen technique is to increase the length of several files on the CD so that they appear to be hundreds of

megabytes long. This is accomplished by setting the file length in the disc image to be much larger than it really is. The file actually overlaps

with many other files. So long as the application knows the true file length, the software will work fine. If the user tries to copy the files

onto their hard drive, or do a file-by-file disc copy, the attempt will fail because the CD will appear to hold a few GB of data. (In practice

 this doesn't foil pirates, because they always do image copies. And, no, none of the standard software provides a way to create such discs.)

One possible implementation, given sufficient control over the reader and mastering software, is to write faulty data into the ECC portion of

a data sector. Standard CD-ROM hardware will automatically correct the "errors", writing a different set of data onto the target disc.

The reader then loads the entire sector as raw data, without doing error correction. If it can't find the original uncorrected data, it

knows that it's reading a "corrected" duplicate. This is really only viable on systems like game consoles, where the drive mechanism

and firmware are well defined. This can be defeated by doing "raw" reads.

A more sophisticated approach is to write special patterns of data to the disc. The stream of data that results, after EFM encoding,

is difficult for some recorders to reproduce successfully, apparently because they don't choose correct values for the merging bits.

This is often referred to on web sites as "writing regular EFM patterns" or "weak sectors". See section (2-43) for details on EFM.

A less sophisticated -- and no longer effective -- method is to press a silver CD with data out beyond where a 74-minute CD can write.

Copying the disc used to require hard-to-find CD-R blanks, but now it's easy to use an overburned 80-minute disc (sections (3-8-1) and (3-8-3)).

The approach some PC software houses have taken is to use nonstandard gaps between audio tracks and leave index marks in

unexpected places. These discs are uncopyable by most software, and it may be impossible to duplicate them on drives that don't

support disc-at-once recording (see section (2-9)). With the right reader and software, though, this isn't much of a problem either.

A method that enjoyed some popularity was non-standard discs with a track shorter than 4 seconds. Most recording software, and

in fact some recorders, will either refuse to copy a disc with such a track, or will attempt to do so and fail. A protected application

would check for the presence and size of the track in question. Some recorders may succeed, however, so this isn't foolproof. (In

one case, a recorder could write tracks that were slightly over three seconds, but refused to write tracks that were only one second.

There may be a limit below which no recorder will write.) In such cases, the pirates need to remove the explicit check from the software itself.

Putting multiple data tracks interleaved with audio tracks on a CD will confuse some disc copiers. However, it's difficult to actually use

 the data on those additional tracks.

Sometimes the copy of a disc will have a different volume label. This usually only happens with file-by-file copies, not disc image copies,

so checking the disc name is marginally useful but not very effective.

Modifying the TOC so that the disc appears to be larger than it really is will convince some copy programs that the source disc is too large.

Some of the fancier technologies use non-standard pit geometry that cause players to read the data differently on consecutive attempts.

Sometimes the player sees a "1", sometimes a "0". If, when reading the track, the CD-ROM drive sees different data each time, the software

knows that the disc is an original. A duplicate disc will return the same data reliably. (So too will some CD-ROM drives... this technology is

not without problems.)

Some programs will examine the disc to try to determine if it's a CD-R. This doesn't work on all readers, and it's possible to disguise discs,

so this isn't very effective.

CloneCD (section (6-1-49)) can copy many copy protected discs without trouble, given the right combination of reader and writer. Its main

 feature is "raw" reads and writes, which not all drives support.

The Laserlok system from http://www.diskxpress.com/ claims to be able to prevent unauthorized disc duplication at a low cost. It can be

copied by CloneCD.

An unrelated product called LaserLock, from MLS LaserLock International (http://www.laserlock.com/) has similar features. It can be

copied by CloneCD.

TTR Technology's DiscGuard (http://www.ttr.co.il/ or http://www.ttrtech.com/ claims to be able to write a signature onto pressed CDs

and CD-Rs that is detectable by all CD-ROM drives but isn't reproducible without special hardware. A program could use this for copy

protection by checking for the presence of the signature, and refusing to run if it's not there.

Sony DADC is promoting a similar product called Securom. Some information is at http://www.sonydadc.com/hotnews/secu_fra.htm.

Yet another variant is C-Dilla's SafeDisc. They were bought by Macrovision (http://www.macrovision.com/). Their more recent product,

SafeDisc 2, was the first to feature "weak sectors".

Yet another variant is CD-Cops from Link Data Security (http://www.linkdata.com/).

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