Why has DVD-10 more capacity than DVD-9 ?

Discussion in 'General Chat' started by plato, Jul 3, 2010.

  1. plato

    plato Well-Known Member


    we have to do an exercise in the course "computer architecture" and the following subtask isn't that easy for me:

    I think it's because on a DVD-9 the two layers can't be placed exactly on top of each other, as there must be some space for the laser while it changes its focus from the first to the second layer.

    My thought doesn't really convince me, so any explanation is much appreciated.

  2. RefCache

    RefCache Well-Known Member

    Because 8.5GB is less than 9.4GB.
  3. plato

    plato Well-Known Member

  4. Carolina Mike

    Carolina Mike Well-Known Member

    DVD-10 is double sided and single layered on both sides.
    DVD-9 is single sided and double layered

    DVD-10 capacity is 9.4 and if you divide that by 2 you get 4.7 GB on each side. Essentially you can think of a DVD-10 to be 2 single sided DVD's.
  5. RefCache

    RefCache Well-Known Member

    The simple elegance AND correctness of my original answer still stands.
  6. plato

    plato Well-Known Member

    I think the question is, why a DVD-9 hasn't 9.4 GB (a DVD-5 has one layer with 4.7 GB and a DVD-9 has two layers, so logically it should have 2*4.7 GB which makes 9.4 GB), but it has 8.5 GB.

    So if somebody is able to explain the "loss" of 0.9 GB capacity, please do so.

    Thank you very much.
  7. Carolina Mike

    Carolina Mike Well-Known Member

    I might be wrong ,but I think it is the Pits (Pits are the slight depressions or dimples on the surface of the disc that allow the laser pickup to distinguish between the digital 1's and 0's. edit:forgot to add where def. came from:http://www.timefordvd.com/tutorial/DVDTutorial.shtml) on both layers are 10% longer than on a DVD-5 or DVD-10 disc. This makes it easier for the laser to read through the disk and get the data. Now if you are 10% bigger then you are storing 10% less data size and thusly that is the data loss difference.
    Last edited: Jul 4, 2010
  8. RefCache

    RefCache Well-Known Member

    That wasn't the question posed though. It was extremely poorly worded. And thus, my original answer still stands.

    And while I'm not proceeding any further in doing someone's homework for them, you should post your prof's e-mail. I'll be happy to contact him/her and explain what a poorly conceived question that is. :)
  9. mike20021969

    mike20021969 Well-Known Member

    This is an interesting question. I cant find the answer anywhere.
    From what I've read, after writing to one of the layers is completed, the other layer is written to by the laser being re-focussed.

    More info: http://www.burnworld.com/howto/articles/intro-to-dual-layer.htm

    I cant find anything regarding differing pit lengths from one layer to the other, although I thought I'd heard something similar before.
    Last edited: Jul 4, 2010
  10. plato

    plato Well-Known Member

    Thank you very much for your strong support.
    It's indeed an interesting question and there is nowhere a direct answer.

    I'll write down Carolina Mike's answer, since it sounds very good to me.

    On Friday they will give us a sample solution and I'll certainly tell you about it.
  11. Spanky

    Spanky Well-Known Member

    The capacity of a DVD doesn't double when you add a whole second layer to the disc. This is because when a disc is made with two layers, the pits have to be a little longer, on both layers, than when a single layer is used. This helps to avoid interference between the layers, which would cause errors when the disc is played. Carolina Mike is correct.
  12. fast eddie

    fast eddie Guest

    Use these capacity's for building a disk and working room. This is good for ALL BRANDS of blank disks.

    DVD-5 single sided, single layer (4.7gb)
    DVD-9 single sided, dual layer (8.5gb)
    DVD-10 dual sided, single layer (4.7gb X 2)
    DVD-18 dual sided, dual layer (8.5gb X 2)


    Always get + plus type blank media, (WHY, burn rate faster, and you can build book type settings)

    If your current player only plays - minus type blank disks, then its time to get a new upscale standard definition DVD player that will play at 1080P thru HDMI
    Last edited by a moderator: Jul 4, 2010
  13. RefCache

    RefCache Well-Known Member

    Judging by your response, you must be the OP's professor.
  14. plato

    plato Well-Known Member

    Who knows?
    But I shouldn't be surprised when I get 0 points on the task because of cheating. :D
  15. DavidS

    DavidS Well-Known Member

    I enjoyed reading this post for the information. Educational.

    Not quite sure how this is 'cheating'. I can see how some might feel a little awkward about it...

    But you were not confined to just reading some book texts... Were you not requested and asked to do RESEARCH so that you could answer the question... ??

    Online research. Filter out all the junk, and figure out the truth... Wiki, Britannical... etc.

    I just found the answer to your question by reading this forum. Only reason - because you asked. So, now it is answered here.... The internet is full of people asking questions, and then others answering. So - going to Slysoft - is doing Research. You would have (and probably did) go/gone elsewhere - if no one here knew the answer...

    And thanks again for the info guys... I enjoyed it. :agree: :clap: