THE DVD


DVD

The next optic drives we will see in the next few years is the DVD drive. They are being developed by several companies (Philips, Sony, and others) and represent a promising technology. DVD stands for Digital Versatile Disk. They are thought of as a future all-round disk, which will replace CD-ROM and laser disks. In the future, DVD might also replace
VHS tapes for videos. Certain DVD drives can both read and write the disks.There are also read only, designed for playing videos.The DVD is a flat disk, the size of a CD - 4.7 inches diameter and .05 inches thick. Data are stored in a small indentation in a spiraltrack, just like in the CD.
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:

Other DVD types

We have the following DVD versions:
  • DVD-ROM is for read-only, like the CD-ROM. This media is usable for distribution of software, but especially for multimedia products, like movies. The outer layers can hold 4.7 GB, the underlying 3.8 GB. The largest version can hold a total of 17 GB.
  • DVD-R (recordable) are write once-only like CD-R. This disk can hold 3.9 GB per side .
  • DVD RAM can be written and read like a hard disk. Capacity is 2.6 GB per side or whatever the agree on. There are many problems with this format.

Movies and multimedia

A 4.7 GB side can hold 135 minutes top quality video with 6 track stereo. This requires a transmission rate of 4692 bits per second. The17 GB disk holds 200 hours top quality music recording.
The following transmission rates are used in the various media:
  • Music on CD requires 150 KB per second. That corresponds to the transmission rate in the first 1X CD-ROM drives.
  • Playing of movies (with a new MPEG-2 compression) requires a transmission rate of about 600 KB per second. That corresponds to the 4X CD ROM drives.
  • Multimedia programmer is expected to provide1.3 MB per second, like a current 10X CD-ROM drive.
DVD movies are made in two "codes." Region one is USA and Canada, while Europe and Asia is region two. When you play movies, your hardware (MPEG decoder) must match the DVD region. The movies are made in two formats, each with their own coding.
Some DVD drive use Dolby AC-3 sound standard. That is a sound system with five full range speakers to surround you with sound, plus a supplementary low frequency special effect channel. To get the full use of the movie sound tracks, you need a AC-3 compatible stereo set up.
The DVD drives come in EIDE and SCSI editions and in 2X, 4X, etc. versions, like the CD-ROM's.
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 5-10 MB/second). No optic media can keep up with this. But the DVD will undoubtedly gain a place as the successor to the CD ROM.

HD-ROM

Futuristic technology. The well-known optical drive types functions using a laser beam. Norsam Technology has developed an other technology where the controlling beam is made of charged gallium ion particles. This gives a very high density, since the beam is very narrow. The new drive technology is called HD-ROM.









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