how information is stored on CDs



How does a smooth little piece of plastic hold possibly like 150gb, it’s not like a hard drive or usb, it’s just a piece of plastic right?

In: Technology

Nope, it’s two smooth pieces of plastic with a layer of super-thin aluminum between them. This aluminum has “holes” punched into it, so that it either reflects light (no hole) or it doesn’t reflect light (“hole”). This lets the disc encode 0 and 1 binary bits in the series of holes/not-holes.

There is a reflective surface on the back of the CD/DVD/BluRay. Pits are made in the plastic on that back side, and a laser is bounced off the reflective surface through the pits and to an eye. The eye reads the pits, and knows what binary data is suppose to be there (1’s and 0’s).

Think of it like old movie film. You sign a light through it, and the image is projected on the screen.

Except it’s happening with very narrow beams of light (lasers) and is bouncing off a reflective surface back to an electric eye watching.

* It’s a piece of plastic with tiny holes etched into it and backed by some reflective paint.
* A laser hits the bottom of the disk and is reflected one way when it hits a smooth part and a different way when it hits one of those holes.
* Smooth versus holes can be encoded as binary data.
* And binary data can represent anything.