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:
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.
Other drives
Here we look at other drive types not previously mentioned:
Super floppies
With the increasing performance in magnetic hard disks you may expect a similar development in the production of the floppy drives. However,it took many years to get alternatives to the 1.44 MB floppy disk. Now we have three drives to choose from, all using special 3½ inch media.
All of them perform very well and are stable and pretty fast:
Drive
Capacity
Comments
Iomega Zip
100 MB
10 million sold units makes it the most compatible drive
LS120
120 MB
Read and write on 1.44 MB floppies as well
Sony HiFD
200 MB
Read and write on 1.44 MB floppies as well
Use the Zip, the LS120 or the HiFD in new PCs - they are cheap and good for backup. You also find portable PC Card versions of these drives.
The Zip drive
The Zip drive uses a kind of diskette, which can hold 100 MB. In my opinion, the Zip drive works excellently. They are stable, inexpensive, and easy to work with. The drives are not the fastest.
I and many others have used Zip drives since they came on the market. This provides us with a common standard to move large files and to make back-ups. For example, you can use this drive to install Windows 95/98 on a computer without a CDROM and avoid having to insert numerous floppy disks.
