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CD and DVD replication is a process that works by creating discs from scratch. Not to be confused with duplication (the act of burning information onto readymade, commercially-available blank CD-Rs and DVD-Rs), replication relies on the use of molds to produce actual discs that already contain digital data. It is the preferred and recommended mode of mass production for quantities in excess of 500 units.

Replication begins with a painstaking process called glass mastering. In this step, a laser is used to copy data onto a light-reactive glass plate. The plate's photosensitive glaze reacts to the heat of the laser, thus etching several gigabytes worth of digital information for permanent storage.

The data encoded on the glass master comes in binary form, a series of 1s and 0s. While these 1s and 0s may seem like gobbledygook to the average human, it is the language that CD and DVD players understand. Once scored onto the plate via laser, binary information appears as very tiny depressions of varying depths, similar to the grooves on a vinyl record.

Since a glass master cannot be altered once it is completed, great care must be taken when preparing one. As a quality control measure, it has to be made in a clean room environment. Any defects or impurities on the glass master will definitely compromise the integrity and playability of the final CDs or DVDs.

A glass master is considered too delicate to be used for heavy-duty and large-scale disc production. Instead, it is used to create several sturdier, more durable metal molds called stampers. In a process known as stamping or pressing, each stamper is injected with a transparent plastic substance called polycarbonate. The excess plastic is then removed, leaving an exact impression of the mold.

To make the polycarbonate disc suitable for playing, it is then finished with a coat of reflective material. Once the replication process is completed, the disc is finally ready for labeling and packaging.

Replication is considered to be superior to disc duplication. As such, it is regarded as the industry standard. This is because it offers greater consistency in production quality and disc playability than the burning process. In a sense, burning may be likened to photocopying while replication may be likened to cloning. Replicated discs are exact and faithful reproductions of their glass masters; duplicated discs, on the other hand, may differ from their source depending on the quality of the blank media used.

However, due to the complicated and tedious nature of CD and DVD replication, its turn-around or completion time is considerably longer than that of duplication. Depending on the number of copies, discs may be duplicated within a matter of minutes. In contrast, a batch of discs can take two to four weeks to replicate.

Replication is also best left to the experts. Owing to the need for clean rooms and special equipment, the startup expense and preparation can be costlier as well as resource-intensive. But in the long run, replication yields a lower per-unit-cost than disc burning.