does laser read the disc inside-out or outside-in?

Discussion in 'General Electronics Chat' started by PG1995, Sep 3, 2011.

  1. PG1995

    PG1995 Thread Starter Active Member

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    Hi

    I don't know if my memory serves me right but I seem to recall that I read it somewhere that the laser reads the disc outside-in and writes inside-out and that's the reason the disc in, let's say, DVD-ROM revolves at high speed when we just start watching a movie than when the movie is reaching its end. But now the result from googling suggest otherwise. What do you say? Please let me know. Thanks.
  2. R!f@@

    R!f@@ AAC Fanatic!

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    Well! Mostly it's inside out, but sometimes the pickup jumpes to the end due to the way the menu and the interactive materials are loaded from disc to disc.

    At least this is what I have noticed
  3. praondevou

    praondevou Well-Known Member

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    I was curious and opened my DVD-player... yes it's inside out
  4. tom66

    tom66 Senior Member

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    Well in my experience it starts from the inside and goes to the outside, but it depends on where you begin in the film.

    Also I have found my DVD player I was repairing would play for 5 seconds without the disk spinning and would tolerate the disc spinning at less than half the normal speed continually, so I'm surprised that it would have to adjust the speed as the disc plays. But I only tested a few minutes each.
  5. R!f@@

    R!f@@ AAC Fanatic!

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    DVD discs can play even if you hold the disc for a couple of secs due to the fact that the decoder has RAM buffers which stores 5 to 10 secs of video data prior to playing.
    It is the shock proof thingy.
  6. tom66

    tom66 Senior Member

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    Yeah I guessed it would have some kind of look up buffer but this was in a home theatre DVD player, so what, it plays during an earthquake? :p
  7. JDT

    JDT Well-Known Member

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    It always starts from the inside. At the beginning is menu that tells the player what is on the disk. Then, it can jump to some other place on the disk.
  8. Bill_Marsden

    Bill_Marsden Moderator Staff Member

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    When you look at the burn pattern on a writable (yes, you can see it) it is always from this inside. This is good because it also allows for 3½" disks, which are shirt pocket sized.
  9. nigelwright7557

    nigelwright7557 Active Member

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    It starts at the inside because you might be using the smaller cd discs and so there would be no disc at the outside edge.
  10. Potato Pudding

    Potato Pudding Active Member

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    With regard to speed of spin-

    Optical drives spiral out with fixed length sectors as opposed to magnetic drives that sector by angular measure over cylinders.

    That means that where a Magnetic drive rotates at constant RPM - an optical drive reduces rotation speed as it moves out from the center because each spiral is a longer path than the ones inside and holds more fixed length sectors.

    That also means that it has faster seek times near the center because of the fewer sectors and faster rotation.
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