XPost: alt.comp.os.windows-11   
   From: G6JPG@255soft.uk   
      
   On 2025/11/19 20:20:51, ...w¡ñ§±¤ñ wrote:   
   > J. P. Gilliver wrote on 11/18/2025 5:37 PM:   
   >> On 2025/11/18 18:18:7, ...w¡ñ§±¤ñ wrote:   
      
   []   
      
   >>> 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   
      
   Ah, understood - so to make it possible to both read through and be   
   readable-through, they use a lower density (in both directions). that   
   explains why only 8.5.   
      
   >   
   How long was/is the maximum for DVD5?   
      
   >   
   > Unlike DVD10 (9.4GB) Double-sided single layer on each side, 4.7GB per   
   > side, requires flipping the disk.   
   >   
   Which (for that reason) presumably wasn't common; I don't think I've   
   ever seen one. Only used for very long movies?   
      
   >   
   _Was_ (is?) there a double sided, double layer variant (DVD11 maybe)? Or   
   were (are) that-long movies just usually supplied on two discs?   
      
   >   
   (What were DVDs 1-4 and 6-8?)   
      
   >   
   --   
   J. P. Gilliver. UMRA: 1960/<1985 MB++G()ALIS-Ch++(p)Ar++T+H+Sh0!:`)DNAf   
      
   cookery seems to be the new sex. - Michael Buerk in RT, 2017/1/21-27   
      
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