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1. How are CD-Rs made?
2. How are CD-RWs made?
3. How is DVD-R/+R made?
4. Physical Characteristics of CD and DVD
5. How is general optical disc made?
6. The physical sizes of CD-Rs and CD-RWs
7. How much information can blank CD-Rs and CD-RWs hold?
8. How many times can a CD-RW disc be rewritten?
9. How much data can actually be stored on CD-Rs and CD-RWs?
10. Glossary: What is lossy?
11. Are DVD-R discs compatible with my reader?

1. How are CD-Rs made?

The first step in producing a CD-R disc is to create the polycarbonate plastic substrate using an injection molding process. The dye layer is made by spin coating and the reflective layer by means of cold planar magnetron sputtering. Additional durability or printable layers are typically made using screen printing methods.

2. How are CD-RWs made?

As with CD-Rs, producing CD-RWs includes a series of steps such as injection molding, sputtering, spin coating, ultraviolet curing and quality inspection, and so on. The first step is to create the substrate by injection molding. The dielectric layers, phase change recording and reflective layers are applied to the substrate by means of cold planar magnetron sputtering. Spin coating and ultraviolet curing are then used to apply the protective lacquer coating.

3. How is DVD-R/+R made?

The first step in manufacturing a DVD-R or DVD+R disc is to fabricate the polycarbonate plastic substrates (incorporating the spiral groove and land pre-pits) using an injection molding process. The dye is then applied using spin coating and the metal layers by means of DC sputtering. After both sides of the disc are completed they are bonded together using a hot melt, UV cationic or free radical process. Additional decoration or printable layers are typically applied using screen printing methods. A DVD-R (General) disc undergoes a further manufacturing step in which a specialized computer DVD recorder is used to "prewritten" information in the Control Data Zone of its Lead-in Area to inhibit direct copying of prerecorded DVD-Video discs encrypted with the Content Scrambling System (CSS). Apart from this, and some minor differences in the configuration of the molding stamper used to create the substrates, the process for manufacturing DVD-R and DVD+R discs is virtually identical.

4. Physical Characteristics of CD and DVD

A CD is a disc with a diameter of 120 mm a thickness of 1.2 mm. The central hole, used to center the CD, has a diameter of 15 mm. It stores 700mb of data.It consists of a disc made of polycarbonate (a material with greater solidity and which resists better to high temperatures than regular plastics). A stacking ring (0.27 mm high) protects the CD-Rs when they are stacked on top of one another and to avoid sticking to each other with static in between. The stamp holder groove has no specific function.

DVD-Video is a standard developed by DVD Forum and specifies how video should be stored on optical DVD disc. DVD-Video specs allow two different kind of video encoding algorithms to be used: MPEG-2 and MPEG-1. Virtually all DVD-Video discs use MPEG-2 format, mostly because of its superiority over MPEG-1 in terms of video quality. DVD can store 4.7GB of data.

By the first quarter of 2006, HD-DVD (high density) and Blue-ray DVD, which have much higher storage capacity, is marketed to the general public. Check out all blank media at thetechgeek.com

5. How is general optical disc made?

Very precise equipment is required for the production of a CD or DVD. It starts with the production of one CD or DVD, the glass master. A powerful laser writes the information on a light-sensitive layer. The parts exposed to laser light are etched away, thus giving rise to the pit pattern. This positive master is used to make a negative die from nickel. This 'stamper' has bumps at the places where pits are to be made in the CD or DVD.

When the stamper is ready, it is installed in the core of the CD/DVD press. The negative die forms a part of the mold that is used to cast the disc. The CD is casted by heating plastic (polycarbonate) and injecting it into the mold. When the plastic has cooled, it leaves a disc in the mold that has a precise imprint of the pit pattern. This disc then passes to the following station in the machine to be given a reflective aluminum layer on the side with the pit pattern. This layer causes the laser light to be reflected when the CD/DVD is played. Major difference between production of CD and DVD is that DVD needs to bond a plastic disc molded with the pit to another disc plated with the reflective when CD is done all on the same disc. This is to give DVD higher capacity. In the following process step the disc is coated in a protective transparent lacquer. The lacquer prevents the aluminum from oxidizing and ensures that the CD or DVD remains antistatic. In most cases a label is then printed on the blank disc in the same machine.

All of this must be carried out with great precision. A single particle of dust can potentially cause irregularities and subsequently lead to hitches in the music. In the early days expensive cleanrooms were required to allow the equipment to operate unhindered and, because every person carries a lot of dust with them, the specialist technologists were dressed like astronauts so as to prevent any risk of contamination.

6. The physical sizes of CD-Rs and CD-RWs

CD-R and CD-RW discs come in standard 12 cm (120 mm) and 8 cm (80 mm) sizes. The most popular is the larger 12 cm type which has the same physical dimension as most commercial audio CDs and computer software CD-ROMs. 8 cm discs are less common but, thanks to their smaller size, are gaining popularity for use in consumer electronic devices such as portable compressed digital audio players, digital still image cameras and data storage products like miniature CD recorders.

7. How much information can blank CD-Rs and CD-RWs hold?

Manufacturers generally express disc capacity in terms of how much Red Book digital audio (in minutes) and computer data (in megabytes) a disc can contain. Historically, 63 minute/550 MB (12 cm) and 18 minute/158 MB (8 cm) discs were once available but are now rendered obsolete by advances in recording technology. Currently, 74 minute/650 MB, 80 minute/700 MB (12 cm) and 21 minute/185 MB (8 cm) discs are the market standards.

8. How many times can a CD-RW disc be rewritten?

As is the case with all optical storage media using phase change technology there is a limit to the number of times the recording layer in a CD-RW disc can be reliably switched between its crystalline and amorphous states. Currently, CD-RW discs can be rewritten approximately 1000 times.

9. How much data can actually be stored on CD-Rs and CD-RWs?

The amount of information that can be written is determined by the disc's recording capacity as well as the physical and logical formats used.

Each of the five main CD physical formats devotes a different amount of space to user data (audio = 2,352 bytes/block, CD-ROM Mode 1 = 2,048 bytes/block, CD-ROM Mode 2 = 2,336/bytes/block, XA Form 1 = 2,048 bytes/block, XA Form 2 = 2,324 bytes/block). For any given data format disc capacity can be calculated by multiplying the appropriate user data area size by the CD data transfer rate of 75 blocks per second by 60 seconds by the minute size of disc. For example, a 80 minute disc written in CD-ROM Mode 1 format: user data area of 2048 bytes/block x 75 blocks/second = 153,600 bytes/second x 60 seconds = 9,216,000 bytes/minute x 80 minutes = 737,280,000 bytes. This rounds to roughly 700 MB (dividing by 1,024 to convert into KB and again by 1,024 to convert into MB). It should be noted, however, that in the real world capacity could vary slightly among discs from different media manufacturers.

For discs written with computer data the logical format used also consumes space available for user information. For example, the overhead for the first session of a multisession disc consumes 22 MB of space and each subsequent session thereafter uses 13 MB. And in the case of CD-RW discs which are formatted for random packet-writing, usable capacity is reduced by roughly 23%.

10. Glossary: What is lossy?

Lossy is a term to describe compression techniques that throw away data as part of the process. The more data "loss", the smaller the file, and the lower the quality (grainy or jagged edged) image. Lossy compression methods include JPEG and MPEG. Note: with JPEG, "high" means high compression (greater loss) and "low" means low compression (less loss). Lossy is used to denote a form of compression that degrades the quality of the image being compressed.

11. Are DVD-R discs compatible with my reader?

DVD-R is the most widely compatible of the various DVD-recording formats. Most standard DVD-ROM drives (over 90%, along with all combo -/+R burners) should be able to read it but there are too many different models out there for me to verify. Really, it shouldn't be that much of a worry but, if you're concerned, I suggest you enter the brand and model of your drive into the Google search box, along with terms such as "DVD-R format compatible". Or you could visit the website of your drive's manufacturer as they usually have a format compatibility chart available.

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