DVD Technology: Overview

  • Last Modified on: September 26, 2007
  • Article: 24451

This article provides information and a general overview of DVD technology, particularly as it relates to Apple products. Included in the article are the following sections:

DVD Background

DVD is an audio/video/data storage standard based on high-density optical discs. DVD includes six major formats:

  • DVD-Video for video data
  • DVD-ROM (Read Only Memory) for computer data
  • DVD-R (recordable) for write-once computer data
  • DVD-RAM for erasable computer data
  • DVD-RW for rewriteable computer data
  • DVD+RW for rewriteable computer data
  • DVD+R (recordable) for write-once computer or video data
  • DVD+R DL (recordable, dual-layer) for write-once computer or video data
DVD-Video audio/visual playback only
DVD-ROM computer data read only
DVD-R computer data (see Notes 2, 3) recordable
DVD-RAM computer data erasable (see Note 4)
DVD-RW computer data rewriteable (see Note 1)
DVD+RW computer data rewriteable

Notes:

  1. DVD-RW discs can be used with third-party utilities (see article 42718 "SuperDrive: About Rewriteable DVD Discs" for additional information).
  2. DVD-R discs can be used by iDVD and DVD Studio Pro to record DVD-Video discs.
  3. DVD-R discs can be used in Mac OS X 10.1.2 or later to record data from the Finder or other applications.
  4. DVD-RAM discs cannot be read or written to using a SuperDrive.

 

DVD Discs

DVD disks are offered in many different capacities ranging from a single-sided, single-layer disk with 4.7 GB of data to a double-sided, double-layer disk with 17 GB of data stored on the disk.

DVD discs can hold nearly 26 times the amount of data that can be stored on a conventional CD-ROM disc. This capacity virtually eliminates the need to swap discs in the middle of a game or application, and at the same time reduces the cost and the number of discs necessary to hold the data. The chart below illustrates the difference between CD and DVD storage possibilities.

CD-ROM 120 mm SS 650 Megabytes Max 74 min audio
DVD-5 120 mm SS/SL 4.7 Gigabytes Over 2 hours of video
DVD-9 120 mm SS/DL 8.5 Gigabytes Approx. 4 hours
DVD-10 120 mm DS/SL 9.4 Gigabytes Approx. 4.5 hours
DVD-18 120 mm DS/DL 17 Gigabytes Over 8 hours
Table Notes:
SS=Single Sided, SL=Single Layer, DS=Double Sided, DL=Double Layered

 

DVD Layers
To squeeze all this information onto the CD-sized disc, the designers of the DVD disc made several changes from the compact disc. The pits and lands used to record data and the track spacing became nearly half the size of the original CD design. The discs were made double sided and another data layer was added to each side, creating a potential for four layers of data per disc.
 
 
CD and DVD pits
Compared to CDs, DVDs use smaller pits and a more closely-spaced track. The result is a significant increase in data density.

Like a CD, a DVD is 120 mm in diameter. Like a CD, a DVD is 1.2 mm thick, made up of two 0.6 mm substrates bonded together. Most DVD-ROM drives are able to play existing audio CDs, although this is not part of the DVD specification.

The DVD standard defines a disc that maintains the overall dimensions, look and feel of the current CD. Some of these similarities provide similarities for customers who have not used DVD disks.

 

Disc Diameter 120 mm 120 mm
Disc Thickness 1.2 mm 1.2 mm
Disc Structure Single substrate Two bonded 0.6 mm substrates
Data Layers 1 1 or 2
Data Capacity Approx. 680 MB Single Layer: 4.7 GB x 2
Dual Layer: 8.5 GB x 2
Data Transfer Rate Mode 1: 153.6 KB/second
Mode 2: 176.4 KB/second 		1,108 KB/second, nominal

DVD-ROM and DVD-Video Discs

DVD disks use the UDF format. The difference between a DVD-ROM title and DVD-Video title is only the data that is stored on the disc. This is one reason why the UDF format was adopted. Discs can be used for different purposes without requiring a change in format.

An Apple DVD-ROM drive can read a DVD-Video disc. However, the computer must be able to decode the video in order for it to be played. The decoders commonly used to compress DVD-Video data are:

  • MPEG-1 or MPEG-2 for video data
  • AC-3 for audio data

Decoding can be performed through hardware or software solutions:

  • Hardware decoding usually includes either a PCI Card that has the MPEG-2 and AC-3 decoders on the card or, for the PowerBook G3 Series DVD, a PC Card with the same equivalent hardware. MPEG-1 can be decoded by QuickTime and does not require hardware decoding.
  • Software decoding does not require any additional hardware because it uses a software-based MPEG-2 and AC-3 decoder.

Related documents

58770 "CD-RW and SuperDrive: Specifications and Usage Information"
60796 "Power Mac G4: SuperDrive Ejects DVD-RAM Discs"
60793 "DVD-R for Authoring Versus DVD-R for General Media"
106610 "Mac OS X: "The disc 'Ram' could not be modified" Alert"
301551 "About optical disc drive burning and write speeds"

Keywords: krefspec ktech