DVD & CD Information

DVD

DVD originally stood for Digital Video Disc (and now sometimes Digital Versatile Disc) although this is not official, and is an optical storage method capable of storing data, video and audio. DVD's have the same physical appearance of CD's (Compact Discs) but can store a much greater amount of data, using a different encoding format and encode at a higher density.

DVD-5: A 12cm single-sided DVD can hold 4.7GB of information, or 8.5GB if dual-layered (DVD-9).
DVD-10: A 12cm double-sided DVD can hold 9.7 GB of information, or 17.1GB if dual-layered (DVD-18).
DVD-5: An 8cm single-sided DVD can hold 1.4GB of information, or 2.6GB if dual-layered (DVD-9).
DVD-10: An 8cm double-sided DVD can hold 2.8GB of information, or 5.2GB if dual-layered (DVD-18).

DVD's come in recordable and non-recordable formats, originally used for data storage and now used mainly for media, film and video presentation.

DVD Formats

Non-recordable:
DVD-ROM: ROM stands for Read Only Memory, and these discs are pressed in a similar way to CD's, with silver or gold reflective surfaces. They can single or double sided, or a combination of both on different sides.
DVD-D: This is a self-destructing form of DVD, which is stored vacuum packed, and begins to oxidise shortly after contact with oxygen. Used for rentals, short-time play content, and protected content trials, this format is not commonly used and some countries have raised concerns regarding the environmental impact of it's usage.
DVD PLUS: These discs are a combination of CD and DVD layers, combining both aspects. Advantages being that the disc can still be recognised by some older CD Player devices that have not yet been designed to deal with DVD.

Recordable:
DVD-R AUTHORING: A specialist form of disc used to record master DVD's, from which batches are duplicated at duplication plants.
DVD-R GENERAL: A fairly generally used recordable DVD format, capable of holding 4.5GB of data and played in most DVD-ROM compatible players.
DVD-RW: Similar to a CD-RW disc, this format can record up to 4.7GB.
DVD-R DL: This is a double-layered form of DVD-R, capable of storing up to 8.5GB of data.
DVD-RAM: RAM stands Random Access Memory. These are usually found in a speacil housing, and require a specialised player to play the 4.7GB or 9.4GB data content. 2.6GB versions can be removed from the housing and played in a regular DVD drive.

Replication

Disc replication is done in a number of steps. First a glass master is created, from the original master disc supplied from the client. This glass master is then used to create a nickel stamper. This stamper is then used to injection mould clear optical discs (polycarbonate substrates).

This process is quite different from disc 'duplication', which is outlined below.

Duplication

This process involves burning content onto blank media such as CDR or DVDR discs, and does not involve the creation of a master or stamper. It is therefore suited to smaller quantities of discs.

CD

A CD (which stands for Compact Disc) is an optical storage disc, for digital data (originally digital audio). CD's were later adaption for use as CD-ROM discs which could store significantly larger quantities of data. CD Drives use an optical sensor to read CD disc layers and the data content within.
CD's are made from polycarbonate plastic, 1.2mm thick, with a thin layer of super purity aluminium (or rarely, gold) applied to the surface and protected by a film of laquer. Printing methods for CD cover art and label art are silk-screening and offset printing.

Data on a CD is stored in a series of tiny indentations (or pits) encoded in a spiral of pits in the top layer of the disc. In between the pits are areas known as 'lands'.

The most common size of CD is 120mm in diameter, with typically a 74 or 80 minute capacity for music, or a 650-700MB data capacity. Singles were released on 80mm discs, which can hold 21 minutes of audio, or 184MB of data.

CD Formats

CD+G: This specialist graphics format contains images as well as the audio content, used mainly to display lyrics on-screen in concert with the songs being played.
CD-R: These are a recordable format of CD, produced by injection moulding with laquer coating. Recordings on these discs are permanent, and the discs can be read in most basic audio CD and CR-Rom players.
CD-ROM: A data-compatible version of the audio CD, with the same physical format, but capable of recording and playing data on CD-ROM drives in most computers.
CD-RW: This a re-recordable CD format, enabling the data to be wiped and re-recorded multiple times. The write laser uses heat to wipe, and rewrite the metal alloys in the CD layers. The lands and bumps in such discs are not as pronounced, so regular CD players often cannot read them, although regular DVD players can. They can prove to be unreliable, also.
MINI-CD: These are smaller, 80mm discs, capable of holding 24 minutes of music, or 210MB of data. Sometimes used for Singles, or referred to as Maxi CD's, these were originally used as pocket-storage before flash drives were introduced.
BUSINESS-CARD CD: A chopped version of the 80mm Mini-CD, this business-card shaped disc can hold anything from 30MB to 100MB of data. Round versions can be produced, in the form of a 60mm disc.

Disc Cases

Jewel case: A three-piece plastic case for CD's or DVD's, with a hinge and space for sleeve notes and a back card. The front piece of plastic has raised marks to keep the front cover sleeve in place. The back tray snaps into place into the front cover, and is responsible for holding the disc, with a circle of gripping teeth that go through the centre spindle.
Slimline Jewel Case: A much slimmer version of a jewel case, for sleek appearance and space-saving purposes. Most are roughly have the thickness of a standard jewel case. They often cannot hold a full peper pamphlet with information, but just a thin cover sleeve. These cases are normally made from the same polystyrene that the jewel cases is made from, although polypropylene is a stronger alternative.
Paper/Tyvek Sleeve: A transport friendly and sust-protective paper and plastic sleeve, enabling a view of the disc labelling. The evelope can also be made from polythylene, a less abrasive and tougher material.
Digipack: A cardboard folding case, into which a plastic disc holder is glued. Used sometimes as a environmentally friendly alternative to plastic cases, they are still not used as much, due to their decreased durability and protection. They can also cost more to make.
LP Style Case: Basically a mini version of the original cardboard LP folders, sometimes with scaled down version of the original LP packaging artwork. Discs held in these kind of sleeves benefit from some kind of protective sleeve, as removal from the LP Style Case can damage the disc over time.
Keep Case: The most commonly used style of DVD cases, slightly taller than the jewel cases, and made of softer plastic for more flexibility. Some of these cases have disc holders on both of the insides.
Box Sets: Designed for episodic tv shows or multiple disc releases, these cases have a thicker spine and can hold up to 10 or 16 discs. Sometimes the discs are overlapping, and there are internal leaved trays for extra discs.
Tri-Slim Jewel Case: A fairly unique kind of disc presentation case, with a piece of car slipped into the front sleeve to hold a third disc in place.