XPost: alt.comp.os.windows-11   
   From: winstonmvp@gmail.com   
      
   J. P. Gilliver wrote on 11/18/2025 5:37 PM:   
   > On 2025/11/18 18:18:7, ...w¡ñ§±¤ñ wrote:   
   >> J. P. Gilliver wrote on 11/18/2025 6:22 AM:   
   >>> You're welcome.   
   >>> I think virtually all movie DVDs were (are, for the small market that's   
   >>> still making and buying them!) dual-layer, except for very short movies.   
   >>>   
   >>   
   >> Movie DVD's have been available in two flavors   
   >>    DVD9 - dual layer which provides 8.5 GB   
   >>    DVD5 - single layer, 4.7GB   
   >>   
   >> Not all dual layer DVDs are DVD9; all DVD9 are dual layer   
   >>   
   >> Non-movie DVDs are also dual layer DVD+R DL or DVD-R DL   
   >>   
   >>   
   > Interesting that it's not 2×4.7=9.4. Why not?   
   >   
   > (Presumably the ones that are DVD5 are just movies that are short enough   
   > to fit in/on a single layer. What duration corresponds to that?)   
   >   
      
   Physical limitations   
     DVD9 single-sided with two layers on one side of the disk   
      - second layer is read by focusing the laser through the   
   semi-transparent first layer. To reliabily accomplish the data pits(where   
   the data is stored)) on both layers are longer, and the track pitch(space   
   between the tracks storing data) wider.   
     i.e. use more space for data, use more space between data = less   
   storage capacity   
      
      
   Unlike DVD10 (9.4GB) Double-sided single layer on each side, 4.7GB per   
   side, requires flipping the disk.   
      
      
      
      
   --   
   ...w¡ñ§±¤ñ   
      
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