A Master disc is a disc that is supplied to a duplication or replication house for the information to be copied on to blank discs as many times as required. Whether it is audio, software, a presentation or videos. This disc is used as the "master" copy. It is loaded onto the CD/DVD duplication towers, which burns whatever is on the disc its hard drive. It then uses that data on the hard drive and duplicates onto blank media (discs).

A glass master, which is also known as a "stamper" is utilised to stamp all of the data pits into a CD or DVD - this process is called replication. It's called a "glass master" because a circular block of glass is used, in which the data is pressed onto a special chemical coating. This glass block is actually bigger than normal size CD - 240mm in diameter and 6mm thick. The reason for this is because the discs need to be handled in a way so that the sensitive data area is not scathed or damaged. Even minuscule scratches or scathes can affect the quality of the discs to prevent this the glass master is polished until it's perfectly smooth.

The milieu in which the glass mastering process is performed in has to be of the highest and cleanest quality. The room itself is a "Class 100" clean room (this is up to 12 times cleaner than an operating theatre). This room is designed not to allow more than 100 particles per cubic foot of air. Your typical working surrounding or office building consists from 500,000 to 1,000,000 per cubic foot of air - very interesting I hear you say! The main particles that can affect the quality of the glass master are dust, pollen and smoke particles.

The replication process takes a lot longer to complete than the duplication process. It is a cheaper but re-assuring method of copying discs. The duplication, although quicker, is dearer and not as quality assured as the replication process.

Some people like to email or upload data to duplication or replication houses for it then to be created as a master. I would strongly recommend against this as there is potential for the data to be corrupted during transfer. This may not be picked up until it gets to the end user. The duplication/replication house will then be held responsible for faulty data.

When dealing with audio masters you will find that production/record companies prefer to finance the creation of masters. This then becomes the property of the record companies. They tend to have an interest in building their catalogue of albums. They even go as far as not taking on independent artists if they have financed the creation of their master themselves. This deal between the artist and the Production Company is called a "spec" deal.