DVD Fun Facts

DVD Background

                        DVD is an audio/video/data storage standard based on high-density optical
                        discs. DVD includes four 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 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.

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.

                       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 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.