Karbosguide.com - Module 4c3a.

The DVD media


The contents:

  • DVD
  • A CD-like disk
  • DVD+RW

    And on the following page:

  • DVD Video Disk
  • MPEG-2 decoding
  • The players
  • The regional codes
  • DD CD-ROM and other new optic drives
  • Next page
  • Previous page


  • An introduction to the DVD

    The DVD is a high-capacity optic media.

    The DVD standard was developed in the mid 1990s by leading companies like Philips and Sony. DVD stands for Digital Versatile Disk.

    The DVD is an all-round disk, which probably will replace CD-ROM and laser disks. Over a few years DVD should replace VHS tapes for videos as well.

    Some DVD drives can both read and write the disks. The drives are sold in many versions and with many incompatible sub-standards.


    A CD-like disk

    The DVD is a flat disk of the same size as a CD. It holds a diameter of 4.7 inches (12 cm) and is .05 inches (1.2 mm) thick. Data are stored in a small indentation in a spiral track, just like in the CD, only the tracks are more narrow.

    DVD disks are read by a laser beam of shorter wave-length than used by the CD-ROM drives. This allows for smaller indentations and increased storage capacity.

    The data layer is only half as thick as in the CD-ROM. This opens the possibility to write data in two layers. The outer gold layer is semi transparent, to allow reading of the underlying silver layer. The laser beam is set to two different intensities, strongest for reading the underlying silver layer. Here you see a common type DVD ROM drive:

    The DVD drives come in EIDE and SCSI editions and in 5X, etc. versions, like do the CD-ROMs.

    The DVD drives are often bundled with a MPEG-2 decoder. This is required if you want to replay DVD video disks at optimal quality. Some graphics cards like Matrox-G400 MAX come with a Cinemaster-based software decoder. This works together with the graphics accelerator chip and gives reasonable DVD replay quality.

    The DVD drives will not replace the magnetic hard disks. The hard disks are being improved as rapidly as DVD, and they definitely offer the fastest seek time and transmission rate (currently 20-30 MB/second). No optic media can keep up with this nor with the speedy seeks we get from the harddisks.

    But the DVD will undoubtedly gain a place as the successor to the CD-ROM. New drives will read both CD-ROMs and DVDs.


    Various DVD types

    We have several versions of the DVD:

    DVD-ROM

    This is the most simple format made for data read-only. It is like a beefed-up CD-ROM. This medium is usable for distribution of software and other data for PC use.

    The outer layers can hold 4.7 GB, the underlying 3.8 GB. The largest version can hold a total of 17 GB.

    A single layer DVD-5 disk holds 4.7 GB. A dual-layred DVD-9 disk holds 8.5 GB. The dual-sided DVDs are named DVD-10 (9.4 GB) and DVD-18 (17 GB).

    DVD Video disk

    This the most important standard. it is a highly sophisticated and very complex format mixing video, sound and data in a very special format.

    DVD-R

    The Recordable DVD are written once only like CD-R. This disk can hold 3.95 GB per side .

    DVD RAM/+RW

    There a at least three different and in-compatible formats of re-writable DVD. The disk can be written and read like a hard disk or perhaps more like a CD-RW.


    DVD RAM

    Three writable technologies are present at the market:

  • Pioneer has a DVD-Recordable technology placing 3.95 GB per disk.

  • DVD-RAM is a RW-disk from Hitachi and Matsushiti. The 1. generation disks hold 3.6 GB, while the 2. generation hold 4.7 GB. The disks are hold in a special cartridge.

  • The so-called DVD+RW, supported by HP, Sony, Philips, Yamaha, Ricoh and Mitsubishi holds up to 4.7 GB per disk.

    None of the three products are compatible. However, the companies behind DVD+RW control 75% of the market, so I think this will become the new standard.

    It appears that the DVD-RAM disks are extremely sensitive to greasy fingers and other contaminants. Therefore they must be handled in special cassettes, which do not fit into ordinary DVD players.

    HP DVD 3100i

    HP has a DVD+RW drive. It reads and writes 3 GB disks at 1,7 MB/sec. The DVD+RW disks should be readable to ordinary DVD drives.

    3100i is an internal SCSI drive. It reads and writes DVD+RW media at a speed of 1.25X (1.7MB/s), which compares to 11X CD-RW write speed. The drive rotates with constant angular velocity (CAV). Using Adaptec's Direct DVD, you can drag and drop files to DVD disk from Microsoft Windows Explorer.


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    Learn more

    Module 4d about MO drives.

    Please read Module 4e about tape streamers (they are not drives).

    Please read Module 5c about SCSI.

    Please read Module 6a about file systems.

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