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The CD-R (Compact Disk-Recordable) was the first writable CD-ROM. They could only be written to once and were not readable until the disk was finalized (adding the root directory structure). As such, they were considered Write-Once Read-Mostly (WORM) devices. CD-Rs were considered good evidence of legal information since they couldn't be altered after being written. If space allowed, new files could be written to a CD-R after the disk was finalized (adding a new session). However, the existing data became unreadable in standard CD drives; only the new data could be read.
A CD-R is manufactured with molded pits of a predetermined length. This surface is coated with a material that permanently darkens when heated with a laser. The writing laser darkens the material in the appropriate pits to record data. Most audio CD players and CD-ROM drives could read these disks as well as with factory-molded disks. "Burning" is often used to describe the CD-R recording process. As appropriate as it may be, this term emerged years before the CD-R was imagined and was first used for Programmable Read-Only Memory circuits.
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The recorded area of a CD-R can be seen because it is darker than the unrecorded area.
Early CD writers had to write to the CD without interruption. Many CD-Rs were destroyed because background programs interrupted the writing process. Special drivers or other programs were produced to mitigate this problem by shutting down all unnecessary processes while a CD was recorded. It wasn't long before CD writers were developed that could be interrupted while writing.
Initially, the writing speed of CD-R drives was slow, taking about 40 minutes to fill a disk. The fastest drives, labeled as 52x, could write at 7.8 MiB per second and fill a CD in about 1.5 minutes. The modern, faster-writing drives spin the disk at tremendous speed, occasionally causing the disk to shatter. Drives with speeds above 20x only write at full speed along the outer part of the disk because the angular velocity of the disk is lower toward the inner part of the disk.
The average lifespan of data on a CD-R is expected to be about ten years. However, the lifespan of the data can vary even with the same manufacturer.
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A CD-R recorded in 2000 showing dye degradation by 2008
CD-Rs should only be labeled with labels designed for CDs. Since the recorded layer is directly under the label, adhesives can damage the protective lacquer coating and the data layer beneath. Printable CD labels come with a jig to align the label, preventing an off-center label from unbalancing the CD.
Permanent markers have long been used to write on CD-Rs with no known problems. However, heavily marking a CD-R with such a pin could damage the lacquer and the data layer.
CD writing software could usually create a bootable CD. These divided the CD into two partitions. The boot partition usually looked to the computer like a floppy disk. To make such a partition required a bootable floppy disk to copy to the CD. The second partition looked like a regular CD to the computer. On Windows systems, the two partitions had different drive letters.
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