Difference between CD-R and CD-RW.

Until CDs become a museum rarity, it would be nice to remember how CD-R differs from CD-RW. It is these optical media that are familiar to us as "blanks" on which you can record any information that fits into the volume.

CD-R (Compact Disc-Recordable) is a compact disc that allows you to record information on it once.

CD-RW (Compact Disk ReWritable) is a rewritable CD.

The external difference between CD-R and CD-RW is manifested only in one thing: its type is indicated on the box and the surface of the disc. Physical dimensions are standard, any modern optical drive works with both. Today they are used in most cases as bootable CDs (for old OS), a means of exchanging data between systems when another option is impossible, as well as in players. Sometimes important information is duplicated on CD-R: it is impossible to accidentally or deliberately erase it from this medium.

Comparison

So, we save data on a CD-R and later we can only read it, while a CD-RW can be completely erased and written again almost an unlimited number of times. You can endlessly turn these discs in your hands, but you still can't see the differences.

How does a compact disk work? A thin layer of metal is applied to the plastic base, on which spiral tracks with grooves are created during recording, everything is covered with a transparent varnish to protect against physical damage. When read, the laser beam is reflected from the deformed and undeformed areas in different ways, and such signals are interpreted by the receiving device.

This applies to read-only disks. The user must also write down the blanks, so one more layer was added to their design on top of a reflective substrate made of gold or silver film. Its properties determine what is the difference between CD-R and CD-RW.

CD-Rs are organic. During the recording process (called burn-in in home systems), the laser heats certain points until they darken, and when reading, the light from the substrate is reflected more intensely where the information-storing layer has remained transparent.

For CD-RWs, everything is somewhat more complicated: the recording layer is made of a special alloy of metals, which, when strongly heated by a laser, changes from a crystalline state to an amorphous state (in other words, it turns glassy). The refractive power of the material is different in different states, so that the amorphous areas play the role of pits. When erasing, medium-intensity heating returns the layer to its original crystalline state. Likewise, information can be rewritten many times on one disc.

Phase transitions after a certain number of write-erase cycles destroy the material of the recording layer, therefore CD-RWs are considered less durable and reliable media than CD-Rs. However, in practice, optical discs fail only as a result of mechanical damage.

For CD-RW, the minimum recording speed is set, below which the transition of a substance from one state to another is simply impossible. The maximum speed values ​​are regulated for both types: if exceeded, the burn will be of poor quality, the points will be "smeared".

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