The Duplication Process, commonly referred to as “burning”, is copying the contents of one CD or DVD to another disc using a drive with write capabilities. The PC or duplication equipment etches the data onto a recordable CD or DVD disc with a laser small enough to be integrated into a normal PC drive bay. CD and DVD burners and media have been a runaway success due to their portability, convenience, and economy. This method is best for producing limited quantities of copies–more than one, but less than a large commercial run. DVD burners can be either PCs with multiple burners or dedicated duplication machines  also called "duplication towers”.   

Duplication of VHS  

VHS Duplication Centre

The Duplication Process of VHS is made in real time. A master plays and the required quantities of VCRs are recording simultaneously. Each VHS cassette is carefully verified to ensure that video and sound are properly recorded. Video tapes have a recording capacity time between 5 to 180 minutes in SP mode. 

Replication of DVD / CD

The above pictures are used only for illustration purposes. They are not the actual premises

The Manufacturing Process consists of replicating or “cloning” the original master. First, a “Glass Master” is created from the original (DVD-R / CD-R / DLT). Then a set of moulds, or “Stampers,” are made from the master. Stampers act as a blueprint for the replication process; they are mounted into an injection-mould machine, where a replica of the mould is created in the form of a 120-mm plastic disc. The formed disc is then coated with a micro-thin reflective layer of aluminium. Finally, the disc is coated again with a protective lacquer that is first spun onto the disc, and then hardened by ultraviolet light.

Because replication is complicated, it is typically considered only for large runs of at least 1,000 copies. At those volumes, replication produces the lowest per-disk cost and offers the highest possible readability levels. In fact, all commercially distributed entertainment and software CDs and DVDs are produced using replication.