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TITLE
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TOPIC
- DVD Background
- DVD Discs
- DVD-ROM and DVD-Video discs
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:
DISCUSSION
- 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
- MPEG-1 or MPEG-2 for video data
- AC-3 for audio data
- 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 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.
DVD Background
DVD is an audio/video/data storage standard based on high-density optical discs. DVD includes four major formats:
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| DVD-Video |
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| DVD-ROM |
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| DVD-R |
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| DVD-RAM |
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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.
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Layers |
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(video) |
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Table Notes:
SS=Single Sided, SL=Single Layer, DS=Double Sided, DL=Double Layered |
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Figure 1 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. First they made pits and lands used to record data and the track spacing nearly half the size of the original CD design. Then, they made the discs double sided and added another data layer to each side creating a potential for four layers of data per disc. See Figure 1. |
Figure 2 CD and DVD pits |
Compared to CD, DVD uses smaller pits and a more closely spaced track. The result is a significant increase in data density. See Figure 2. |
Like CD, DVD is 120 mm in diameter. Like CD, DVD is 1.2 mm thick composed of two 0.6 mm substrates bonded together. The new DVD-ROM drives are able to play existing audio CDs, however 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.
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| Disc Diameter |
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| Disc Thickness |
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| Disc Structure |
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| Data Layers |
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| Data Capacity |
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Dual Layer: 8.5 GB x 2 |
| Data Transfer Rate |
Mode 2: 176.4 KB/second |
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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:
Decoding can be performed through hardware or software solutions.