Burning CDs

The Layers of a CD-R

A CD-R is not just a piece of plastic – it is an astonishingly precise layer structure:

• Polycarbonate substrate layer with an embossed spiral track (Pregroove / Helix). The track edges are slightly wavy – from this frequency, the recorder reads the rotational speed.
• Recording layer made of organic dye (Cyanine, Phthalocyanine, or Azo).
• Reflective layer made of gold or silver.
• Protective lacquer layer on top – it protects the sensitive reflective layer.

ATIP – Where the Laser Orients Itself

The track contains not only data but also time information: the Absolute Time In Pregroove (ATIP). It tells the burner where it currently is and what the maximum capacity of the blank disc is.

EFM – How 8 Bits Become 17 Bits

During burning, the laser produces patterns of pits and lands (depressions and elevations). Each 8-bit data byte becomes 17 bits on the recording surface – 14 channel bits plus 3 merging bits. This conversion is called Eight to Fourteen Modulation (EFM) and occurs via a lookup table permanently implemented in the drive.

Recording Materials & Colors

The recording layer usually consists of one of three basic compositions – each with its own properties:

• Cyanine (typically blue) – durability approximately 10 years or more
• Phthalocyanine (transparent to slightly green/yellow) – manufacturers state up to 100 years
• Azo (typically blue) – also up to 100 years

The specific final formula is usually a manufacturer's secret. Therefore, one can no longer unambiguously deduce the material from the color of a blank disc – but as guidelines:

• Green: Cyanine + golden reflective layer
• Gray: Cyanine + stabilizers + golden reflective layer
• Golden: Phthalocyanine + golden reflective layer
• Slightly greenish-yellow: Phthalocyanine + silver reflective layer
• Blue: Cyanine or Azo + silver reflective layer

Recording Methods: DAO, TAO & Co.

Disc at Once (DAO)

The professional method: A CD is written in a single session in one pass and then closed – lead-in (with table of contents), all tracks, and lead-out, without interruption. DAO is a prerequisite for clean pause design (e.g., for live recordings) and subchannel interventions like indices.

Track at Once (TAO)

With TAO, the laser is switched off after each track, the preliminary table of contents (PMA) is updated, and then repositioned at the endpoint. This allows tracks to be added piece by piece – the most important method for multisession discs. The disadvantage: subchannel modifications are not possible.

Session at Once (SAO)

A prerequisite for regular CD-Extras: A data session is placed behind a DAO audio session. Both sessions are applied in one go – a technical contradiction in terms, but it works.

Incremental Packet Writing (IPW)

While DAO writes an entire session and TAO writes a track at once, IPW only writes smaller data packets – usually the size of the internal recorder buffer. This almost eliminates the risk of a buffer underrun.

Single- vs. Multisession

• Singlesession Disc: One session, then closed. Audio CDs are by definition singlesession.
• Linked Multisession: Multiple sessions whose tables of contents are linked – appears as a seamless whole. The most common multisession variant.
• Multivolume: Each session is burned as an independent partition, without linking. Access to older sessions only with special drivers.

Storage Capacities of a CD

The capacity of a CD-R is traditionally given in minutes – a legacy from the Red Book for audio CDs. Common playing times:

• 21 min – Single CDs / VIP cards
• 60 min – difficult to obtain
• 74 min – the original standard
• 80 min – currently the standard
• 99 min – special format (see below)

However, the actually usable capacity depends not only on the playing time but also on the CD format:

• Audio CD (CD-DA): 2352 bytes user data per sector → for 74 min ≈ 783 MB
• Data CD (CD-ROM Mode 1): 2048 bytes/sector → for 74 min ≈ 650 MB
• CD-ROM/XA Form 2: 2324 bytes/sector → for 74 min ≈ 770 MB

For 80-minute blanks, proportionally more. Plus: Each blank has 1–4 minutes of tolerance, which can be tapped by overburning.

CD-R (Orange Book)

The Orange Book is the specification for the recordable CD-R. Essentially, it describes how a CD can be written in multiple sessions – previously, a blank disc could only be endowed with a single session, and that was it.

The Orange Book is part of the "Rainbow Books" – the collective term for all CD specifications (Red, Yellow, Green, Orange, Blue, White, Beige, Scarlet, Purple).

90/99 min CDs

99-minute blank discs combine two tricks to exceed the specification:

• Narrower helix tracks (as with 80-minute blanks)
• Overburning – exploiting manufacturing tolerances for 2 to 4+ extra minutes

Why 99-minute blank discs must be overburned

In the ATIP of the blank disc, the maximum playing time is indicated as 79:59 – as with 80-minute media – regardless of the true capacity. The range 90:00 to 99:59 is actually reserved for the lead-in and would have to be addressed in negative values. Sector addresses would be duplicated – many burners therefore refuse to function.

While 99-minute blank discs can also use multisession, you only utilize the full capacity in Disc-at-Once mode in a single session.

Further Variants of CDs

Boot CD (El Torito)

Data CDs from which a computer can boot. Linux and DOS are well suited for this. Windows is out – it wants to write to the boot drive, which doesn't work well with CDs. Prerequisite: a BIOS that allows CD booting at all.

Picture CD

A standard introduced by Kodak to encourage users to develop photos onto CD. Essentially a simple data CD with personal photos plus a graphic viewer. In Germany, the Picture CD is not available – here, there is only Kodak's Photo CD.

VIP Card

A multimedia business card (~80 × 55 mm) based on a single CD. Writable with any CD burner that supports 21-minute blank discs. 12 to 50 MB (more when compressed) for photos, text, music, videos. Often used for marketing or applications.

Hybrid / Janus CDs

Discs that are runnable on both PC (ISO 9660) and Mac (HFS). Two variants:

• Non-shared Hybrid: Both partitions contain the complete data set, strictly separated from each other
• Shared Hybrid: A common data set (e.g., images) plus two OS-specific areas

Treatment & Care of CDs and DVDs

Burned discs are more sensitive than commercially pressed ones – a few simple rules can greatly extend their lifespan.

Definitely avoid:

• Direct sunlight and strong heat
• High humidity
• Fingerprints on the read or write side
• Labeling with ballpoint pens or alcohol-based felt-tip pens (they destroy the lacquer layer)
• Labels or stickers that are not centered
• Harsh cleaning agents
• Hard cloths for dusting
• Makeup brushes or large amounts of alcohol for cleaning
• Blowing on them – this spreads saliva on the disc
• Leaving them unprotected
• Storing important data on only a single CD