And on the following page:
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.
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
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).
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.
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.
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
Copyright (c) 1996-2005 by Michael B. Karbo. www.karbosguide.com.