Once recorded, CD-R discs can be played back or read in any standard CD-ROM drive. CD-R discs are useful for archival storage and creating master CDs, which can be duplicated for distribution within a company. CD-Rs function using the same principle as standard CD-ROMs, by bouncing laser light off the disc and tracking the changes in reflectivity when pit/land and land/pit boundaries are encountered.

The main difference is that instead of being stamped or embossed into plastic as on regular CDs, CD-Rs have images of pits burned onto a raised groove instead. Therefore, the pits are not really raised bumps like on a standard CD, but instead are rendered as dark (burned) areas on the groove that reflect less light.

Because the overall reflectivity of pit and land areas remains the same as on a stamped disc, normal CD-ROM or CD audio drives can read CD-Rs exactly as if they were stamped discs. Part of the recording process with CD-Rs starts before you even insert the disc into the drive.

CD-R media is manufactured much like a standard CD—a stamper is used to mold a base of polycarbonate plastic. However, instead of stamping pits and lands, the stamper imprints a spiral groove (called a pre-groove), into the disc. From the perspective of the reading (and writing) laser underneath the disc, this groove is seen as a raised spiral ridge and not a depression.

The pre-groove (or ridge) is not perfectly straight; instead it has a slight wobble. The amplitude of the wobble is generally very small compared to the track pitch (spacing). The groove separation is 1.6 microns, but it wobbles only 0.030 microns from side to side.

The wobble of a CD-R groove is modulated to carry supplemental information read by the drive. The signal contained in the wobble is called absolute time in pre-groove (ATIP) because it is modulated with time code and other data. The time code is the same minutes:seconds:frame format that will eventually be found in the Q-subcode of the frames after they are written to the disc.

The ATIP enables the drive to locate positions on the disc before the frames are actually written. Technically, the wobble signal is frequency shift keyed with a carrier frequency of 22.05KHz and a deviation of 1KHz. The wobble uses changes in frequency to carry information.

To complete the CD-R disc, an organic dye is evenly applied across the disc by a spin-coating process. Next, a gold reflective layer is applied, followed by a protective coat of UV-cured lacquer to protect the gold and dye layers. Gold is used in CD-R discs to get the reflectivity as high as possible, and it was found that the organic dye tends to oxidize aluminum.

Then, silk-screen printing is applied on top of the lacquer for identification and further protection. When seen from the underside, the laser used to read (or write) the disc first passes through the clear polycarbonate and the dye layer, hits the gold layer where it is reflected back through the dye layer and the plastic, and finally is picked up by the optical pickup sensor in the drive.

The dye and reflective layer together have the same reflective properties as a virgin CD. In other words, a CD reader would read the groove of an unrecorded CD-R disc as one long land.

To record on a CD-R disc, a laser beam of the same wavelength (780nm) as is normally used to read the disc, but with 10 times the power, is used to heat up the dye. The laser is fired in a pulsed fashion at the top of the ridge (groove), heating the layer of organic dye to between 482°F and 572°F (250°–300°C). This temperature literally burns the organic dye, causing it to become opaque.

When read, this prevents the light from passing through the dye layer to the gold and reflecting back, having the same effect of canceling the laser reflection that an actual raised pit would on a normal stamped CD. Figure below shows the CD-R media layers, along with the pre-groove (raised ridge from the laser perspective) with burned pits.

The drive reading the disc is fooled into thinking a pit exists, but no actual pit exists—there's simply a spot of less-reflective material on the ridge.

This use of heat to create the pits in the disc is why the recording process is often referred to as burning a CD. When burned, the dye changes from a reflective to a nonreflective state.

This change of state is permanent and can't be undone, which is why CD-R is considered a write-once medium.

CD-R Capacity

All CD-R drives can work with the standard 650MiB (682MB) CD-R media (equal to 74 minutes of recorded music), as well as the higher-capacity 700MiB (737MB) CD-R blanks (equal to 80 minutes of recorded music).

The 80-minute discs cost only about 2 cents more than the 74-minute discs, so most would figure why not purchase only the higher-capacity media? Although the extra 55MB of storage can be useful and the cost difference is negligible, the 80-minute discs can actually be harder to read on older CD-ROM and CD-DA drives, especially car audio units.

This is because to get the extra 55MB/6 minutes of capacity, the spiral track is wound a little more tightly, making them a bit more difficult to read. If you'll be using the discs for audio or interchange purposes and might be dealing with older equipment, you might want to stick with the 74-minute discs instead. If not, the 80-minute media will be just fine.

Some drives and burning software are capable of overburning, whereby they write data partially into the lead-out area and essentially extend the data track. This is definitely risky as far as compatibility is concerned. Many drives, especially older ones, fail when reading near the end of an overburned disc.

It's best to consider this form of overclocking CDs somewhat experimental. It might be useful for your own purposes if it works with your drives and software, but interchangeability will be problematic. Some vendors now sell 90-minute (790MiB) and 99-minute (870MiB) media to make overburning easier.

Although experiments performed by the Tom's Hardware indicate that most standard CD-RW drives can reliably burn up to 89:59 of music onto the 90-minute media and the CD-R can be played on a wide variety of auto and home electronics players, very few drives can burn a full 90 minutes or more of music (or the equivalent amount of computer data) to this media.

CD-R Media Color

There has been some controversy over the years about which colors of CD-R media provide the best performance. Table below shows the most common color combinations, along with which brands use them and some technical information.

Media Color	Brands	Technical Notes
Gold-gold	Mitsui, Kodak, Maxell, Ricoh	Phthalocyanine dye. Less tolerance for power variations. Has a rate life span of up to 100 years. Might be less likely to work in a wide variety of drives. Invented by Mitsui Toatsu Chemicals. Works best in drives that use a Long Write Strategy (longer laser pulse) to mark media.
Gold-green	Imation (nee 3M), Memorex, Kodak, BASF, TDK	Cyanine dye. More forgiving of disc-write and disc-read variations. Has a rated life span of 10 years (older media). Recent media has a rated lifespan of 20–50 years(silver/green). Color combination developed by Taiyo Yuden. Used in the development of the original CD-R standards. De facto standard for CD-R industry and was the original color combination used during the development of CD-R technology. Works best in drives that use a Short Write Strategy (shorter laser pulse) to mark media.
Silver-blue	Verbatim, DataLifePlus, HiVal, Maxell, TDK	Process developed by Verbatim. Azo dye. Similar performance to green media plus rated to last up to 100 years. A good choice for long-term archiving.

Some brands are listed with more than one color combination, due to production changes or different product lines. You should check color combinations whenever you purchase a new batch of CD-R media if you've found that particular color combinations work better for you in your applications.

Ultimately, although the various color combinations have their advantages, the best way to choose a media type is to try a major brand of media in your CD-R/CD-RW drive with both full-disc and small-disc recording jobs and then try the completed CD-R in as wide a range of CD-ROM drive brands and speeds as you can.

The perfect media for you will be the ones that offer you the following:

• High reliability in writing (check your drive model's list of recommended media)

• No dye or reflective surface dropouts (areas where the media won't record properly)

• Durability through normal handling (scratch-resistant coating on media surface)

• Compatibility across the widest range of CD-ROM drives

• Lowest unit cost

If you have problems recording reliably with certain types of media, or if you find that some brands with the same speed rating are much slower than others, contact your drive vendor for a firmware upgrade. Firmware upgrades can also help your drive recognize new types of faster media from different vendors.

Choosing the Best Media

After you determine which media works best for you and your target drives, you might still be faced with a wide variety of choices, including conventional surface, printable surface, unbranded, jewel case, and bulk on spindle. The following list discusses these options:

• Conventional surface. Choose this type of media if you want to use a marker to label the CD rather than adding a paper label. This type of CD often has elaborate labeling, including areas to indicate CD title, date created, and other information as well as prominent brand identification.

Because of the surface marking, it's not suitable for relabeling unless you use very opaque labels. It's a good choice for internal backups and data storage, though, where labeling is less important.

• Printable surface. Choose this type of media if you have a CD printer (a special type of inkjet printer that can print directly onto the face of the CD). Because the brand markings are usually low-contrast or even nonexistent (to allow overprinting), this type also works well with labeling kits such as NEATO and others.

• Unbranded. Usually sold in bulk on spindle, these are good choices for economy or use with labeling kits.

• Jewel case. Any of the preceding versions can be sold with jewel cases (the same type of case used for CD-ROM software and music CDs). This is a good choice if you plan to distribute the media in a jewel case, but it raises your costs if you plan to distribute or store the media in paper, Tyvek, or plastic sleeves. Hint: Use extra jewel cases to replace your broken jewel cases in your CD software or music collection!

• Bulk on spindle. This media generally comes with no sleeves and no cases. It is usually the lowest-priced packaging within any brand of media. This is an excellent choice for mass duplication, or for those who don't use jewel cases for distribution.

CD-R Media Recording Speed Ratings

With CD-R mastering speeds ranging from 1x (now-discontinued first-generation units) up through the latest state-of-the-art 48x–52x rates, it's important to check the speed rating (x-rating) of your CD-R media. Most branded media on the market today is rated to work successfully at up to 32x recording speeds.

Some brands indicate this specifically on their packaging, whereas you must check the Web sites for others to get this information. If your drive is faster than 32x (new drives are now reaching 48x–52x speeds), look for media that supports the maximum speed of your drive and comes from a manufacturer supported by your drive.

If necessary, install the latest firmware updates to reach maximum recording speed. If speed ratings are unavailable for your media, you might want to restrict your burning to 32x or lower for data. If you are burning audio CDs, you might find that some devices work better with media burned at 8x or lower speeds than with media burned at higher speeds.