# CDs (the audio kind, not the financial kind) **URL:** \ **Category:** Factual Questions\ **Created:** [November 5, 2005, 1:49pm UTC](https://boards.straightdope.com/t/cds-the-audio-kind-not-the-financial-kind/329644 "2005-11-05T13:49:37Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![HeyHomie](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/heyhomie/32/207_2.png) [@HeyHomie](https://boards.straightdope.com/u/HeyHomie)\ **Post date:** [November 5, 2005, 1:49pm UTC](https://boards.straightdope.com/t/cds-the-audio-kind-not-the-financial-kind/329644/1 "2005-11-05T13:49:37Z")
Does the laser on my CD player read the CD from the outside in (like a stylus on a record player), or from the inside out? The information stored on a CD: is it stored on the outside of the disk, with blank space in the middle, or vice-versa? Finally: when my CD burner burns a CD (or when the machinery at the factory does it), does it burn from the outside in, or from the inside out? ---
**Author:** ![Mr.Blue\_Sky](https://avatars.discourse-cdn.com/v4/letter/m/d26b3c/32.png) [@Mr.Blue\_Sky](https://boards.straightdope.com/u/Mr.Blue_Sky)\ **Post date:** [November 5, 2005, 2:10pm UTC](https://boards.straightdope.com/t/cds-the-audio-kind-not-the-financial-kind/329644/2 "2005-11-05T14:10:00Z")
A CD player/burner works from the inside towards the outside on a continous spiral track (just like vinyl records, except in the opposite direction). ---
**Author:** ![neutron\_star](https://avatars.discourse-cdn.com/v4/letter/n/51bf81/32.png) [@neutron\_star](https://boards.straightdope.com/u/neutron_star)\ **Post date:** [November 5, 2005, 2:18pm UTC](https://boards.straightdope.com/t/cds-the-audio-kind-not-the-financial-kind/329644/3 "2005-11-05T14:18:38Z")
> [@HeyHomie](#): > > The information stored on a CD: is it stored on the outside of the disk, with blank space in the middle, or vice-versa? The blank space is on the outside of the disc. If you look closely at an already-burned CD-R (or DVD-R) that’s not completely full, you can see a line where the burn stopped. The spiral track around the disc onto which data is written is 0.5 microns wide. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [November 5, 2005, 3:30pm UTC](https://boards.straightdope.com/t/cds-the-audio-kind-not-the-financial-kind/329644/4 "2005-11-05T15:30:37Z")
Factory-made CDs aren’t burned. That’d be much too slow for mass production. They’re mechanically pressed in a mold, much like vinyl LPs were. One smoosh and the entire CD is done. Then a protective outer layer is put over the pressed dents and the whole thing heated to fuse the cover onto the substrate. ---
**Author:** ![ultrafilter](https://avatars.discourse-cdn.com/v4/letter/u/3d9bf3/32.png) [@ultrafilter](https://boards.straightdope.com/u/ultrafilter)\ **Post date:** [November 5, 2005, 10:47pm UTC](https://boards.straightdope.com/t/cds-the-audio-kind-not-the-financial-kind/329644/5 "2005-11-05T22:47:46Z")
The data on a CD is actually just under the label. The rest of the disc’s thickness is due to a protective layer of plastic. ---
**Author:** ![Fritz](https://avatars.discourse-cdn.com/v4/letter/f/c57346/32.png) [@Fritz](https://boards.straightdope.com/u/Fritz)\ **Post date:** [November 5, 2005, 11:49pm UTC](https://boards.straightdope.com/t/cds-the-audio-kind-not-the-financial-kind/329644/6 "2005-11-05T23:49:51Z")
> [@LSLGuy](#): > > Then a protective outer layer is put over the pressed dents and the whole thing heated to fuse the cover onto the substrate. Sorry, not quite. The polycarbonate substrates are molded as you describe, the data layer is metallized with a thin layer of (usually) aluminum - about 50-70 nanometers thick, then the metallized data layer is spin-coated with a layer of liquid UV-curable resin called lacquer - about 5-12 microns thick. The disc is exposed to very high energy radiation for 1-2 seconds and the lacquer is cured. The finished discs then go to be printed. ---
**Author:** ![Fritz](https://avatars.discourse-cdn.com/v4/letter/f/c57346/32.png) [@Fritz](https://boards.straightdope.com/u/Fritz)\ **Post date:** [November 6, 2005, 12:18am UTC](https://boards.straightdope.com/t/cds-the-audio-kind-not-the-financial-kind/329644/7 "2005-11-06T00:18:30Z")
> [@Fritz](#): > > The disc is exposed to very high energy radiation for 1-2 seconds and the lacquer is cured. Should be: very high energy _ **UV** _ radiation