Welcome to brain Stuff from how Stuff Works dot com where smart Happens. This podcast is brought to you by Audible dot com, the Internet's leading provider of audio books, with more than eighty five thousand downloadable titles across all types of literature. For brain Stuff listeners, Audible is offering a free audio book to give you a chance to try out their service. One audiobook to consider is Steve
Jobs by Walter Isaacson. This biography is based on many personal interviews with Steve Jobs, his family, his friends, and colleagues. Here the real story of one of the greatest innovators of our time. That's Steve Jobs. Available from Audible. To try Audible free today and to get a free audiobook of your choice, get Audible podcast dot com slash brain Stuff. That's Audible podcast dot com slash brain Stuff. Hi Im Marshall Brain with today's question, how do SDR discs work?
If you've read the how Stuff Works article describing how c ds work, then you know that the basic idea behind data storage on a normal c D is simple. The surface of the CD contains one long spiral track of data. Along the track, there are flat, reflective areas and non reflective bumps. A flat reflective area represents a binary one, and a non reflective bump represents a binary zero.
The CD drive shines a laser at the surface of the c D and can detect the reflective areas and the bumps by the amount of laser light they reflect. Normal c ds can't be modified. There read only devices. A CDR disc needs to allow the drive to write data onto the disk. For a CDR disc to work, there must be a way for a laser to create a non reflective area on the disk. A CDR disc therefore has an extra layer that the laser can modify.
This extra layer contains a greenish dye. In a normal c D, you have a plastic substrate covered with a reflective aluminum or gold layer. In a CDR, you have a plastic substrate, a die layer, and a reflective gold layer. When you write data to a CDR, the writing laser, which is much more powerful than the reading laser, heats up that die layer and changes its transparency. The change in the dye creates the equivalent of a non reflective
bump on the surface of the disk. This is a permanent change, and both a CD and a CDR drive can read that modified die layer as a bump. Later on, it turns out that the dye is fairly sensitive delight. It has to be in order for a laser to modify it quickly. Therefore, you want to avoid exposing CDR discs to sunlight. This podcast is brought to you by audible dot com, the internet leading provider of audiobooks, with more than downloadable titles across all types of literature and
featuring audio versions of many New York Times bestsellers. To try Audible free today and to get a free audio book of your choice, go to audible podcast dot com slash brain Stuff. That's Audible podcast dot com slash brain Stuff. The Howstuff Works iPhone app has arrived. Download it today on iTunes