DVD ROM's

Digital Versatile Disc (DVD):

• DVD originally designed for use as DVD-video, but now can be used as DVD-Audio and DVD-ROM
• Most beneficial when used as DVD-ROM
• Allows for enhanced multimedia, and game applications
• Backwards capability with CD's- can read CD's and CD-ROM's
• Same dimensions as a CD,  but uses two .6 mm thick substrates bound together
• Single/Dual -layer option, with single/ double side option as well
• 4.7 GB read-only capacity per layer/ 8.5 GB per side
• An entire 2-hour movie can be stored onto one DVD
• Allows for higher quality music- even allows for surround sound
• Includes built-in digital copy protection
• Comes in recordable, re-recordable versions

  Types of DVD's: 
 

Name	Capacity(GB)	Layers	Sides
DVD-5	4.7	1	1
DVD-9	8.54	2	1
DVD-10	9.4	1	2
DVD-18	17.08	2	2
DVD-R	4.7/9.4	1	1 or 2
DVD-RAM *	2.6/5.2	1	1 or 2
DVD-RW**	4.7	1	1 or 2

* rewritable
**re-recordable

DVD-ROM's versus CD-ROM's:

•  7-8 CD-ROM's are needed to store the same amount as 1 DVD-ROM

= Pictures from disctronics * not to scale

• All DVD-ROM's have the same file system versus CD-ROM's that use separate systems compatible with different operating systems (eg MAC, Windows/DOS)
• CD-ROM's only have one layer of data storage while DVD-ROM's have two layers.
• Pit sizes in DVD-ROM's are half that of CD-ROM's
• DVD's have a higher mastering speed than CD's
• Different manufacturing process are needed to allow for two layers, causes increase in cost for DVD's versus CD's

A single CD (either -ROM, or -R) costs about $1 to purchase, while a single DVD-RAM costs about $40.  Unfortunately, despite the great advantages to DVD's they are still very expensive compared to CD's.

Why doesn't everyone just use DVD's then???

DVD File Systems:

   DVD's have a different directory structure than CD's.  Titles that include more than one media (eg. video & PC-game) would have data stored in more than one directory.  The separate directories allow for easier and faster retrieval of information.

Image courtesy of disctronics
 

Manufacturing of DVD's:

• Very similar to CD manufacturing
• 2 -substrates are needed for the dual layer recording
• Photo-resist layer should be about 120 nm thick
• Laser used must be much smaller - UV laser
• CSS (Content Scrambling System)- provides copyright protection and is carried out during the mastering stage.  Data is combined with encrypted keys and then scrambled
• Two pressings (fathers) needed for each DVD- each half is 0.6 mm thick
• Two halves must be molded together
• Data is always stored in the middle of the disk, so that double sided disks are possible

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Last edited on May 14, 2000