Slide 4.11: CDs (Compact Discs)
Slide 4.13: Flash memory
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DVDs (Digital Versatile Discs)

A DVD is an optical storage medium with improved capacity and bandwidth compared with the CD. DVD, like CD, was initially marketed for entertainment and later for computer users. It holds a minimum of 4.7 GB of data, enough for a full-length movie. DVDs are commonly used as a medium for digital representation of movies and other multimedia presentations that combine sound with graphics.

The table on the right lists DVD formats available today, where
  • DS – double sided;
  • DL – double layer;
  • SL – single layer; and
  • SS – single sided;
Name Format Data
Capacity		 Video
Capacity
DVD-5 SS/SL 4.7 GB 2+ hours
DVD-9 SS/DL 8.5 GB 4 hours
DVD-10 DS/SL 9.4 GB 4.5 hours
DVD-14 DS/multiple layer 13.24 GB 6.5 hours
DVD-18 DS/DL 17 GB 8+ hours
DVD-RAM SS/SL 2.58 GB N/A
DVD-RAM DS/SL 5.16 GB N/A
Blu-Ray DS/DL 30 GB 15 hours
HD-DVD DS/DL 20 GB 10 hours

A DVD can hold a full-length film with up to 133 minutes of high quality video, in MPEG-2 format, and audio. The first DVD drives for computers were read-only drives (“DVD-ROM”). These provide over seven times the storage capacity of CD-ROM (4.7 GB). Additionally, DVD-ROM drives read existing CD-ROMs and music CDs and are compatible with installed sound and video boards.

Write-once DVD-R (“recordable”) drives record a 3.9 GB DVD-R disc that can be read on a DVD-ROM drive. The first DVD-R drive was expected by mid 1997. DVD_RAM drives read and write to a 2.6 GB DVD-RAM disc, read and write-once to a 3.9 GB DVD-R disc, and read a 4.7 or 8.5 GB DVD-ROM. Also, it was expected that a DVD-RAM disc would be readable on both the DVD-R and DVD-ROM drives.