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Understanding DVD

The advantage of DVD’s over CD's are...

  • 5 to 6 times the capacity
  • longer shelf life
  • faster retrieval

Both CD's and DVD's store data in microscopic grooves running in a spiral around the disc. Reflective bumps (lands) and non-reflective highs (pits) aligned along the grooves represent the zeros and ones of digital information.

DVD technology writes in smaller pits by reducing the laser's wavelength from 780mm to 625-650mm, resulting in higher capacity. In addition, the DVD tracks are closer together.

DVD's access data faster than CD and users more error correction. A DVD 1x is faster than 8x CD.

Most DVD’s can read CD’s and CD-R’s, so the transition from CD to DVD is simple. It is important to understand the different types of DVD drives (here we go with more abbreviations, sorry)...

DVD Types
  • DVD-RAM- Random Access Memory (Read and Write)
  • DVD-R or DVD+R Recordable (Only write one time)
  • DVD-RW or DVD+RW Re-recordable or Rewritable (Read and Write)
  • DVD-ROM Read Only Memory (Read Only)
Random versus Sequential
  • DVD-RAM uses random access technology
  • DVD-R, +R, -RW, +RW or ROM use a sequential technology.

Random Access: DVD-RAM (Read & Write)

  • Can be used as the ideal technology for backup or storage. Unlike tape storage that can only read data sequentially, DVD-RAM can access data randomly just like a normal hard drive. This makes a selective recovery process much easier and faster.
  • Can be overwritten up to 100,000 times.
  • Provides 4.7GB (Type 2) per side storage capacity or 9.4GB (Type 4) two-sided.
  • Life expectancy of 100 years.
  • Can only be written and read with DVD-R/RAM drives.
  • Since first introduced in 1998, the price for has dropped from $2,000 to less than $500.
Sequential: DVD-R, +R, -RW, +RW or ROM

This group of DVD’s are intended for the hi-tech graphics, video for movies and audio for music. They provide better quality for graphics and sound along with higher capacity of 4.7GB.

Writable: One Time
  • DVD-R
    • Can only be written with -R type drives.
    • Can be read with -R or +R type drives.
  • DVD+R
    • 2 hours of video in SP mode or 4 hours in EP mode
    • Can only be written with +R type drives.
    • Can be read with -R or +R type drives.
Writable: Re-writable up to 1000 Times
  • DVD-RW
    • Contains protection technology that prevents copying of CSS-protected discs.
    • Can only be written with -R type drives.
    • Can be read with -R or +R type drives.
  • DVD+RW
    • Can hold 2 hours of MPEG2.
    • Can only be written with +R type drives.
    • Can be read with -R or +R type drives.
Read Only
  • DVD-ROM
    • Can only be used for reading.
    • Movies you buy or rent are usually DVD-ROM.
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