CD-R (redirected from compact disc write-once)

(CD-Recordable) A writable CD technology using a type of compact disc that can be recorded, but not erased (CD-Rs are "write once" discs). CD-R discs are used to master CD-ROMs, to back up data and to make copies of data for distribution. "Burning" a CD-R requires a CD-R drive, CD-RW drive or a combo CD/DVD drive. CD-R discs can be read on most every type of CD drive, including older CD-ROM units.

In practice, the term "CD" refers to all CD formats. The phrase "burn a CD" really means "burn a CD-R."

One at a Time
CD-R drives are called "one-off" machines, because they write one disc at a time, unlike the CD manufacturing process that stamps them out by the thousands. However, high-end CD-R duplicators with multiple drives can make hundreds of copies per day and can also print the labels.

Capacities
To record a full 650MB disc (74 minutes) takes only a couple minutes using 40x recorders, but considerably longer with earlier drives. In 1998, 700MB discs (80 minutes) added only a few minutes of audio, but 50MB more for data. In 2002, 800MB CD-R media (90 minutes) was introduced. The additional storage capacity is achieved by reducing the distance between tracks (track pitch). For detailed speed ratings of CD-RW drives, see CD-ROM drives.

Every time more data is squeezed onto the medium, there is no guarantee that all older drives will reliably support the new format, thus 100% interchange is not guaranteed.

Change the Reflectivity
CD-Rs create the equivalent of pits in the disc by altering the reflectivity of a dye layer. Different dyes can be used, including cyanine (green), pthalo-cyanine (yellow-gold) and metal-azo (blue). See CD-RW, multisession, disc-at-once, track-at-once, CD UDF and optical disc.

CD-R and CD-ROM Layers

Both gold and silver are used for the reflective layer on a CD-R disc. Fresh out of the box, a CD-R disc is entirely reflective lands, because the dye layer is transparent. In order to create the equivalent of a pit, the laser deforms the dye, making it darker and less reflective. On CD-ROMs, the lands and pits are molded into the plastic which is covered by an aluminum reflective coating. To see how a laser reads a CD-ROM, see CD-ROM.

A Partially Burned CD-R

Recording starts at the CD's center and spirals outward. You can tell if a CD-R was burned by looking for the slight change in reflectivity on the recording side. In this example, the arrow points to the end of the small recorded area; less than 6% of the total 700MB.

Burning a CD-R

To "burn" a CD-R disk using Easy CD Creator, you drag the required files and folders into the recording window (bottom). The software supports audio and data CDs and also prints the front cover and inside jacket of the jewel case.

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CD-R - Compact Disc Recordable