CD-R

Alternatively referred to as a cd writer, CD-WO (write once), or WORM (write once read many), CD-R is short for Compact Disc-Recordable. It is a writable disc and drive that is capable of having information written to the disc once and then having that disc read many times after that. Data cannot be deleted from a CD-R disc and a CD-R disc cannot be formatted. If the data is not written to the disc properly, it cannot be corrected and is often jokingly referred to as a coaster.  The first recordable specification CD-WO (write once) was published in 1989 by Philips and Sony in the Orange Book. However, the drives were not popularized until Hewlett Packard released the HP 4020i in September 1995, which was the first sub $1,000.00 recordable disc drive.   CD-Rs are a low-cost solution for backing up software and only costs a few cents (as of 2018 around 19-cents a disc) and can hold up to 700 MB (80 minutes of music). Although these are still a very popular solution for backing up data, more users are turning to DVD-R, USB thumb drives, and the cloudto backup and transfer data.

How does the CD-R work?

A CD-R disc is coated with a photosensitive organic dye that allows a user to record information. Once the CD-R disc is placed in the computer, the recording process begins. The laser inside the drive heats the dye to reveal areas that diffuse the light like a traditional CD pit. The CD-R drive does not create pits on the CD; instead, the burner creates reflective sections on the CD causing the computer's CD-ROM laser to interpret it as a pit. Once a CD-R disc is finished recording, the CD can be used in any standard CD-ROM, CD-R, CD-RW, or DVD drive. Although there were issues with the first revision DVD drives reading CD-R disc, today's drives no longer suffer from any reading problems.

R/W

R/W may refer to any of the following:

1. Short for Read/Write, R/W is a file attribute or permission that can be given to files and directories that allows them to be read or written. These attributes can also be taken away to prevent that file from being read or modified.

2. Short for Read/Write, R/W is a drive and CD media that was first introduced in 1997 that is capable of being written to and read. Unlike a traditional CD-R disc that can only be written to once, these discs allow data to be erased and re-written multiple times.

How does a CD-RW work?

The CD-R technology uses a photosensitive dye. CD-RW discs use an active layer of Ag-In-Sb-Te (silver-indium-antimony-tellurium) alloy that, in its original state, has a polycrystalline structure that makes it reflective. When the CD-RW drive writes to the disc, the laser uses its highest power setting known as Pwrite. At this temperature, which is usually between 500 and 700 degrees Celsius, the chemical structure will liquefy. In its liquid state, the molecules of the active material flow freely, losing their polycrystalline structure and taking on an amorphous state. When the material solidifies in this amorphous state, it loses its reflectivity. By selectively firing the laser, the drive leaves parts of the disc in its polycrystalline state, forming the lands, and parts in the amorphous state forming the pits.  To reverse the phase of a specific area on a disc, the laser operates at a lower power setting and heats the active material to approximately 200 degrees Celsius. By heating the disc, it reverts back from its amorphous to its polycrystalline state and then becomes reflective again.  The drawback with CD-RW discs is with the lower reflectivity of the disc itself can limit the readability. In the 1980s, the CD standards specified that on a compact disc the lands should have a minimum of 70% and the pits should have a reflectance of 28%. However, on a CD-RW disc, the reflectance of a land is approximately 15% to 25%. The low reflectance can cause certain CD-RWs discs to be unreadable in some older CD-ROM drives and CD players.