A CD recorder, CD writer or CD burner is a compact disc drive that can be used to produce compact disc readable in other CD-ROM drives and audio CD players. A DVD recorder produces DVD discs playable in stand-alone video players or DVD-ROM drives. They are generally used for small-scale archival or data exchange, being slower and more materially expensive than the moulding process used to mass-manufacture pressed discs.

A recorder encodes (or burns ) data onto a recordable CD-R, DVD-R or DVD_plus_R disc (called a blank ) by selectively heating parts of an organic dye layer in the disc with a laser in its write head. This changes the reflectivity of the dye, thereby creating marks that can be read as with the pits and lands on pressed discs. The process is permanent and the media can be written to only once.

For rewriteable CD-RW, DVD-RW and DVD_plus_RW media, the laser is used to melt a crystal metal alloy in the recording layer of the disc. Depending on the amount of power applied, the substance may be allowed to melt back into crystalline form or left in an amorphous solid form, enabling marks of varying reflectivity to be created. Most rewriteable media is rated by manufacturers at up to 1000 write/erase cycles.

The competing DVD+R and DVD-R disc formats use very similar dye-based media, but differ mainly in the way timing hints for the write head are laid out on the disc surface. This is also the case with DVD+RW and DVD-RW.

Most internal CD recorders for personal computers, server systems and workstations are designed to fit in a standard 5.25 drive bay and connect to their host via an Advanced Technology Attachment, SATA or SCSI bus. External CD recorders usually have USB, FireWire or SCSI interfaces. Some portable versions for laptop use power themselves off batteries or off their interface bus.

SCSI recorders are less common and tend to be more expensive because of the cost of their interface chipsets and more complex SCSI connectors.

= Compatibility =

= Performance =

Early-model recorders were CLV (constant linear velocity) drives. The recording speed on such drives was rated in multiples of 150 KiB/s; a 4X drive, for instance, would write steadily at around 600 KiB/s. The transfer rate was kept constant by having the spindle motor in the drive run about 2.5 times as fast when recording at the inner rim of the disc as on the outer rim.

There are mechanical limits on the maximum angular velocity at which discs can be spun: at 25000 RPM and beyond, the tensile stress on the disc can expand small manufacturing defects in the disc polycarbonate and then cause the disc to warp and shatter.

To keep the rotational speed of the disc safely low, more recent high-speed recorders tend to use the Z-CLV (zoned constant linear velocity) scheme. This divides the disc into stepped zones, each of which has its own constant linear velocity. A Z-CLV recorder rated at 52X , for example, would write at 20X on the innermost zone and then progressively step up to 52X at the outer rim.

In the late 1990s, buffer overruns became a very common problem as high-speed CD recorders began to appear in home and office computers, whichfor a variety of reasonsoften could not muster the I/O performance to produce a data stream to keep the recorder steadily fed. The recorder, should it run short, would be forced to halt the recording process, leaving a truncated track that often renders the disc useless.

In response, manufacturers of CD recorders began shipping drives with buffer overrun protection (under various trade names, such as Sanyo s BURN-Proof , Ricoh s JustLink and Yamaha s Lossless Link ); these can suspend and resume the recording process in such a way that the gap the stoppage produces can be dealt with by the error-correcting logic built into CD players and CD-ROM drives.

The DVD+R and DVD+RW disc formats were designed with discontinuous recording in mind because they were expected to be widely used in digital video recorders. Many such DVRs used variable-rate video compression schemes which required them to record in short bursts; some allowed simultaneous playback and recording by alternating quickly between recording to the tail of the disc whilst reading from elsewhere.

== See also ==

*Overburning *ISO image *Compact disc, CD-R. CD-RW *DVD, DVD-R, DVD_plus_R, DVD-RW, DVD_plus_RW *CDDA, ripping

= External links =