Deconstructing Technology

Pits And Lands

The CD is one of those technologies that seems to be…lingering. In fact, it’s on our A-T Technology Death Pool. But what of that shiny surface?

As you may already know, it’s made up of “pits” which are usually 100 nm deep and 500 nm wide and vary from 850 nm to 3.5 µm in length. Between the pits are “lands”. However, these don’t translate directly to 1s and 0s. Instead, the change from pit to land or land to pit indicates a 1 and the length of the pit or land determines how many 1s or 0s there are. The data is encoded in a technique developed by Phillips called eight-to-fourteen modulation, and this same technique is used by your CD player to read the data back. It allows for longer playing time than if it was just a Morse-code style 1 and 0 method, and provides some robustness to allow the disc to still work if (mildly) scratched.

[Image Credit: drewdaniels.com]

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  • PowerTryp

    That's really cool to know, but it leads me to ask what makes DVD's and BluRay have larger capacities?

    • http://o2richenvironment.blogspot.com/ engineerd

      If I remember right, the pits and lands are much smaller and they use a different compression algorithm.

      • craigsu

        I thought they had multiple layers as well.

        • http://o2richenvironment.blogspot.com/ engineerd

          That, too. With more powerful lasers!

          • FЯeeMan

            and sharks! never forget the sharks!

    • BlackIce_GTS

      BluRay uses a blu(e) laser. Blue light has a shorter wavelength than red, so they can make the dips smaller.

      • http://o2richenvironment.blogspot.com/ engineerd

        I knew somebody would step up with an answer.

        You forgot the sharks, though.

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