7.1 How is an HD DVD-ROM disc constructed?
7.2 How is an HD DVD-R disc constructed?
7.3 How is an HD DVD-RAM disc constructed?

How is an HD DVD-ROM disc constructed?
Similar to conventional DVD-ROM construction, an HD DVD-ROM (prerecorded) is a sandwich of multiple layers of materials with either one or two data sides (single or double-sided) each with one or two data layers (single or dual-layer). A single-sided (SS) disc is composed of a data side and a dummy side while a double-sided (DS) disc consists of two data sides.

The data side of a single-layer (SL) disc begins with a substrate (polycarbonate) molded with a spiral track of pits and lands extending from the inside to the outside diameter of the disc. Added to this substrate is a reflective layer (aluminum or silver alloy). The dummy side consists of an additional flat substrate (polycarbonate). An adhesive layer then bonds the data and dummy sides (for a single-sided) or two data sides (for a double-sided) together into the final disc.

For a single-sided (SS) dual-layer (DL) disc, first comes a substrate with its track of pits and lands [data layer 0] and a semi-reflective layer (silver alloy). The second substrate is molded with another track of pits and lands [data layer 1] followed by a reflective layer (silver alloy). A transparent adhesive spacer layer then bonds the two sides together.

A double-sided (DS) dual-layer (DL) disc is more complex. Each data side consists of a substrate imprinted with pits and lands [data layer 0], a semi-reflective layer (silver alloy), a transparent spacer layer imprinted with a second track of pits and lands [data layer 1] with a reflective layer (aluminum or silver alloy). An adhesive layer then bonds the two data sides together.

How is an HD DVD-R disc constructed?
Just like an HD DVD-ROM (prerecorded), an HD DVD-R (recordable) disc can be either single (SS) or double (DS) sided each with single (SL) or dual (DL) layers. A single-sided (SS) disc is composed of a recording side and a dummy side while a double-sided (DS) disc consists of two recording sides.

The recording side of a SL disc begins with a substrate (polycarbonate) molded with a shallow spiral groove extending from the inside to the outside diameter of the disc. Next a recording layer (organic dye or inorganic material) followed by a reflective layer (silver alloy). The dummy side consists of an additional flat substrate (polycarbonate). An adhesive layer then bonds the recording and dummy sides (for a SS) or two recording sides (for a DS) together into the final disc.

The recording side of DL disc is more complex consisting of a substrate imprinted with the shallow spiral groove, a recording layer [data layer 0], a semi-reflective layer, a spacer layer imprinted with a second groove, a second recording layer [data layer 1] and a reflective layer. An adhesive layer then bonds the recording and dummy sides or two recording sides together.

How is an HD DVD-RAM disc constructed?
An HD DVD-RAM disc is single-layer (SL) and can be either single (SS) or double (DS) sided. A SS disc is composed of a recording side and a dummy side while a DS disc consists of two recording sides.

The recording side begins with a substrate (polycarbonate) molded with a shallow spiral groove extending from the inside to the outside diameter of the disc. Pits and lands are also included in the grooves and on the areas between the coils of the grooves (land and groove). Next are two dielectric layers (zinc sulfide and silicon dioxide followed by silicon dioxide or silicon oxide and carbon), a thermal control layer (aluminum nitride), another dielectric layer (zinc sulfide and silicon dioxide), a phase change alloy recording layer (germanium, antimony, tellurium and bismuth), a final dielectric layer (zinc sulfide and silicon dioxide) and a reflective layer (silver alloy). An adhesive layer then bonds the recording and dummy sides (SS) or two data sides (DS) together.