How is information and data read from a compact disc?

A CD writer burns little holes in an aluminum disk (between 2 plastic plates).

This causes little bumps to appear on the disc.

A CD drive can read the data back out using a laser that reflects on that surface.

in a bump the laser will reflect in a different angle then when there isn't a bump.

the CD drive detects this and reads a '1' if the laser is not reflected (no bump) and a '0' if the laser is reflected (hits a bump).

This method of storing data contains a lot of errors, bumps that are read wrong.

That's why a CD contains 2/3 fault checks on the actual data.

This means that on a CD you can actually write 2.1 GB of data, but only 700mb is the data you store because 1.4gb is used to repair the mistakes in reading.