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]