DVD and CD: The Basics

A mass-produced DVD/CD (recognizable by its silver color), for example an AudioCD or a CD-ROM, is a non-magnetic, polished metal disc which is used to store digital information. Tiny indentations have been pressed in this disc, which are called pits. In a DVD/CD drive this disc is scanned by means of a laser beam. Because the pits reflect the light from the laser differently than the rest of the surface, the drive can interpret surface and pits as binary information; ones and zeros. The information on such a disc can only be read; no data can be added (or deleted) afterwards.

What makes a recordable disc, such as a CD-R or DVD-R, different from an ordinary DVD/CD is a layer of organic dye that has been added to a perfectly smooth reflective surface. In the DVD/CD recorder a laser beam is used to burn a pattern in the organic dye. When you place the disc in the DVD/CD-drive, these burns cause changes in the reflection of the laser light in much the same way as do the pits on a manufactured disc. Any DVD/CD-drive can therefore read the information you write on a recordable disc. Once written, these burns cannot be deleted. Each part of the disc can therefore be used only once. You can, for instance, use recordable discs to create pre-master discs that can be used to mass-produce DVDs/CDs in a mastering and replication plant.

The information on a Rewritable disc (CD-RW or DVD-RW) can be erased to make place for new data. The surface of such a disc can be smoothed by means of a separate, high intensity laser beam in the recorder, preparing the disc for reuse. In this way a CD-RW or DVD-RW can be used many times. DVD+RW and DVD-RAM are media that can be randomly overwritten, without the need for erasing the media first.

DVD: Concepts and Standards

The ever increasing need to store very large amounts of data on a portable medium has led to the development of the Digital Versatile Disc (DVD). A DVD, although the same size as a CD, can hold 4.7 - 17 GB of data, compared to the 650Mb that a CD can hold. For this reason it is now widely regarded as the successor of the CD.

DVD disc capacity

The increase in storage capacity of DVD has first of all been made possible by enhancing the density of the disc, which brought the capacity to 4.7 GB. However, DVDs will soon become available in double sided and dual layer versions. The effects of these innovations on DVD disc capacity are shown in the table below:

Applications

DVD is the right format for applications in the fields of:

Video - DVD-VIDEO disc can hold a movie (and its sound track) of approximately 133 minutes, providing a resolution that surpasses current S-VHS standards.

Audio - DVD-AUDIO will put an end to the limitations of music CDs and provide the listener with playback sound of a quality that closely approaches that of a live performance.

Multi-media - DVD-ROM will greatly facilitate the use of real video, high resolution graphics and truly interactive scripts in multi-media productions, effectively eliminating any restrictions to the size of such applications.

DVD-R, DVD-RW, DVD+RW, DVD+R, and DVD-RAM

For writing DVD media, there currently are several types of drives and media available:

DVD-Recordable (DVD-R), DVD-Rewritable (DVD-RW), DVD-plus-Rewritable (DVD+RW), DVD-plus-Recordable (DVD+R), and DVD-RAM.

DVD-R is fully compatible with DVD-VIDEO and DVD-ROM formats, including a disc capacity of 4.7 GB. This makes DVD-R a good choice for archiving purposes and the creation of multi-media productions including DVD-Video. DVD-RW (DVD minus RW) is the rewritable DVD format introduced by Pioneer (with the PioneerDVR-A03/A04 drive).

DVD+RW (DVD plus RW) is a slightly different rewritable DVD format recently introduced by Ricoh, Philips, Sony, HP and other manufacturers. DVD+R is the latest format released, being a read-only variant of DVD+RW.

Finally, DVD-RAM is a random access technology for DVD, that initially offered computer users 2.6 GB of re-usable storage space on each side (5.2 GB for double sided discs). Recently the 4.7 GB capacity per side has also been established for DVD-RAM.

Universal Disc Format (UDF)

The way files are organized on a CD-ROM or DVD-ROM (and even DVD-Video) is determined by the file system. The file system defines, for example, levels in a directory tree or the length and format of the file names. A standard file system ensures the exchange of data between different computer platforms.

The file system used to store data on CD-ROM (ISO 9660, optionally with Joliet) proved to be inadequate to make full use of the storage potential of DVDs. To remedy this, a new CD/DVD file system standard was developed by the Optical Storage Technology Association (OSTA): Universal Disc Format (UDF).UDF has been further refined in order to maximize data interchange, and creating a flexible format that is eminently suited for incremental writing.

Besides creating CDs and DVDs in pure UDF format, GEAR Pro DVD allows you to create hybrid ISO 9660 / UDF CDs and DVDs, being backward compatible with ISO 9660.

Excerpted from Gear PRO Professional Edition User Manual. Follow this link to learn more about Gear PRO Professional.