Illustration 1.1 Stamped CD


 

How Optical Drives Write

Some Optical Drives have the ability to write (Burn) information onto a disk. This is accomplished by the use of a second more powerful “Write Laser”. The write laser interacts with the “dye” layer (see illustration 1.2) of a recordable disk.
 

Illustration 1.2 Typical CD-R


 

In its natural state the die layer is transparent allowing light to pass through that layer and be reflected back from the Aluminum layer. When you heat the dye layer with concentrated light of a particular frequency and intensity, the dye turns opaque: It darkens to the point that light can't pass through.

By selectively darkening particular points along the CD track, and leaving other areas of dye translucent, you can create a digital pattern that a standard CD player can read. The light from the player's laser beam will only bounce back to the sensor when the dye is left translucent, in the same way that it will only bounce back from the flat areas of a conventional CD. So, even though the CD-R disc doesn't have any bumps pressed into it at all, it behaves just like a standard disc. The one drawback is this technology is not perfect as older drives may not be able to read CD-R discs burned in this fashion.

Rewritable Technology

CD-RW discs have taken the idea of writable CDs a step further, building in an erase function so you can record over old data you don't need anymore. In CD-RW discs, there is a special compound unlike that of a CD-R disc that can change opacity more than once (See Illustration 1.3). As with any physical material, you can change this compound's form by heating it to certain temperatures. When the compound is heated above its melting temperature (around 600 degrees Celsius), it becomes a liquid; at its crystallization temperature (around 200 degrees Celsius), it turns into a solid.

 

Illustration 1.3 Typical CD-RW
 

In a CD-RW disc, the reflecting and non-reflecting bumps of a conventional CD are represented by the changes in the opacity of the special compound. When the compound is in a crystalline state, it is translucent, so light can shine through to the metal layer above and reflect back to the laser assembly. When the compound is melted into a liquid state, it becomes opaque, making the area non-reflective.

Media Introduction

Media is the actual storage item, typically a disk. There are many different types of media. eMachines currently supports the following physical formats.

Manufactured (Stamped) Compact Disk (CD): A manufactured disk is a disk that is not burned. The information is stamped into the aluminum layer of a disk then covered with a label. This type of disk is Read only and is the most compatible in all readers.

• Read Only
• 700 megabytes
• Highly Compatible
• Very Durable

Compact Disk Recordable (CD-R): A CD-R can be written to with a CD Recorder Drive. The disk is considered “Write Once Read Many (WORM)” because its surface area can only be written to once, but read many times.

• Write Once Read Many
• 700 megabytes
• Compatible with most modern readers

Note: With the use of multi-sessions, recorders can stop the burning process and begin again in non-burned area until the unburned area is used up. This requires 21 MB of overhead space.

Compact Disk Rewritable (CD-RW): A CD-RW is very similar to the CR-R but has the ability to be written to and erased up to a theoretical 1000 times.

• Write Many Read Many
• 700 megabytes
• Only compatible with computers and CD-RW rated players

Manufactured (Stamped) Digital Versatile Disk (DVD): A Manufactured disk is a disk that is not burned. The information is stamped into the aluminum layer of a disk then covered with a label. A DVD can store information on up to four layers. Two layers per side.

• Read Only
• Up to 16 Gigabytes of storage space
• Highly Compatible
• Very Durable

Digital Versatile Disk Recordable (DVDR): A DVDR can be written to with a DVD Recorder Drive. The disk is considered “Write Once Read Many (WORM)” because its surface area can only be written to once, but read many times.

• Write Once Read Many
• Up to 4.7 Gigabytes of storage space
• Compatible with most modern readers

Digital Versatile Rewritable (DVD-RW): A DVD-RW is very similar to the DVD-R but has the ability to be written to and erased up to a theoretical 1000 times.

• Write Many Read Many
• Up to 4.7 Gigabytes of storage space
• Only compatible with computers

DVD-R/W (Dash) Vs. DVD+R/W

There are two competing DVD Recording standards, DVD-R/W and DVD+R/W drives have similar features and are compatible with many standalone DVD Players.

DVD-R and DVD-RW

• DVD-R/W was the first DVD recording format released that was compatible with standalone DVD Players.
• DVD-R is a non-rewriteable format and it is compatible with about 93% of all DVD Players and most DVD-ROMs.
• DVD-RW is a rewriteable format and it is compatible with about 77% of all DVD Players and most DVD-ROMs.
• DVD-R/W supports single side 4.7 GB* DVDs (called DVD-5) and double side 9.4 GB* DVDs (called DVD-10).
• These formats are supported by DVD Forum.

DVD+R and DVD+RW

• DVD+R/W have some "better" features than DVD-R/W such as lossless linking and both CAV and CLV writing.
• DVD+R are a non-rewritable format and it is compatible with about 87% of all DVD Players and most DVD-ROMs.
• DVD+RW are a rewritable format and are compatible with about 77% of all DVD Players and most DVD-ROMs.
• DVD+R/W supports single side 4.7 GB* DVDs (called DVD-5) and double side 9.4 GB* DVDs (called DVD-10).
• These formats are supported by the DVD+RW Alliance.

Optical Drive Specifications

Compact Disk ROM (CD-ROM) Drive

A CD-ROM Drive is capable of reading both Audio and Data Compact Disks with its one “Read Laser”. The original 1x CD-ROM reads at 150 kbps. The next generation of drives were able to read twice as fast (300 kbps) which is where the name 2X came from. Modern drives are able to read at 58X or 58 times faster than the original drives. A recently added feature is the ability to make a compact disk “Bootable”.

In eMacInfo2, compact drives are usually represented by a single speed for example a 58X CD-ROM would be represented like:

Primary Optical : 58X

Note: Audio compact disks still read at 1X (150 kbps).

Compact Disk Recorders (CD-R/RW)

The first CD Recorders where able to Write to a CD-R and read Compact disks. Latter the ability to Erase and write again (Re-Write) was introduced. The burning is accomplished with the help of a second laser. The “Write Laser” is a higher power laser that interacts with a recordable layer on a CD-R or CD-RW. In eMacInfo2 Recorders are usually represented by three speeds for example a drive that Writes at 20x Rewrites 10x and Reads at 40x would be represented like:

Primary Optical : 20x10x40x

Digital Versatile Disk ROM Drives

DVD is short for Digital Versatile Disc or Digital Video Disc, a format which holds 4.7 GB or more of data. The drives are backward-compatible with CD-ROMs, and some models can read CD-R and/or CD-RW discs. With these features and declining DVD drive prices; these drives are rapidly replacing CD-ROM drive hardware in many new systems. Video is written using the MPEG2 format and include a region code. Region codes are a tag that is encoded on the disk that makes the disks only readable by a drive with the same region codes. These region codes allow major motion companies to control the release of a movie in an area normally defined as a country. In eMacInfo2, DVD drives are usually represented by two speeds for example a drive that reads compact disks at 48x and reads DVD disks at 16x would be represented like:

Primary Optical : 48x16x

MPEG2:
A variant of the MPEG video and audio compression algorithm and file format, optimized for broadcast quality video. MPEG-2 was designed to transmit images using progressive coding at 4 Mbps or higher for use in broadcast digital TV and DVD.

DVD+R and DVD+RW Drives
Offering roughly seven times the storage capacity of a CD-ROM, DVD recorder drives are now doing for video what CD recorders did for music. With a DVD writer, you can records up to 3 hours of video or save photos, music, or data to a 4.7GB DVD disc, making DVD+R/RW discs the ideal media for high-volume data backup. DVD+R is a write-once media similar to CD-R, while DVD+RW is a rewriteable media similar to CD-RW. DVD+R media costs less than DVD+RW, has an archival life of up to 100 years, and cannot be erased, accidentally or otherwise, making it an excellent choice for long-term storage. DVD+RW, on the other hand, has the advantage of being reusable. In addition DVD+R is usually compatible with a wider range of hardware than DVD+RW media. DVD+R/RW discs and recorders have been steadily dropping to affordable consumer price levels. Some available models can write CD-R and CD-RW discs as well as DVD. DVD Burners are typically displayed as:

Primary Optical : 20x4x10x2.4X40x

Application Formats

In addition to the many physical formats available you must also consider the content of the disk. Depending on the content and the way the information is laid out on the disk will determine the “Application format”

• Audio CD (80 Minutes of Audio)
An audio CD stores up to 80 minutes on a regular disk in the file format CDA (Compact Disk Audio). CDA is very similar to uncompressed Wave file formats.

• Data Compact Disk (700 Megabytes of Data)
Data CD can store a file in any format. The Data CD is used most commonly for Data back up and Distribution. The files can sit inside Folders in much the same way they are held on a Hard Drive.

• Video Compact Disk: VCD (45 minutes of Video)
Video is encoded into MPEG1 and stored on a regular Compact Disk. This file format was first introduced just before DVD but due to its relative low quality of video and limited space, was eventually replaced by DVD.

• Super Video Compact Disk: SVCD (About 30 minutes of video)
Similar to VCD but files are recorded in MPEG2. Image and sound quality is equal to DVD but the quality cuts down on the amount of video that can be contained.

• Mini-Digital Versatile Disk: Mini-DVD (About 20 minutes of Video)
Exact same format as DVD but stored on a regular 700 MB compact disk.

• Digital Versatile Data Disk: DVD (4.7 Gigabytes of data)
Information is stored in files and folders much like the Data CD, but due to the DVD’s extremely small data footprint and compression. DVD disks can contain up to 4.7 Gigabytes.

• Digital Video Disk: DVD (120 Minutes of video per layer)
DVD disks are becoming commonplace in the industry. Data is stored in folders and in MPEG2. This provides the ability to include chapter search, interactive menus etc, all with excellent picture and audio quality.