CD-R (Compact Disc Recordable) AWRITE-ONCE version of the CD-ROM disc, which can be used to distribute and back up computer data or to copy music CDS. Though it follows the same data format and can be read in standard CDROM drives, CD-R employs quite a different physical storage process, based on an organic dye film that is selectively bleached by a laser beam, which explains the blue or green colour of the recording surface.
Recording a CD-R, often called burning it, requires a special DRIVE called a CD Writer, which can also read conventional CD-ROMs (recent models may also write CD-RW discs). Writing to a CD-R disc is a delicate REAL TIME operation and even a short interruption to the process, say by another program using too much processor time, can cause the resulting disk to be unreadable (sometimes called 'burning a coaster' in an allusion to the only use for such disks).
Data written to a CD-R can be deleted (i.e. made unreadable), but not removed or altered. Most CD-Rs are now MULTISESSION so, if not full, more data can be recorded later but, in contrast to the CD-RW, the existing data cannot be overwritten.