2 Replies Latest reply: Sep 11, 2013 2:06 PM by Ardwa
Ardwa Level 1 (0 points)

The question is in the title!


Thank You

Mac mini, OS X Mountain Lion (10.8.2)
  • Joe Bailey Level 6 (12,205 points)

    Not all optical drives are created equal. Commercial CDs are mechanically stamped creating microscopic pits in the surface of the media that change the reflective characteristics of the surface and the resulting reflection and no reflection of the read laser that is interpreted as a binary digital signal that is interpreted as sound. Generally very few drives have a problem reading these mechanically stamped discs. Burned CDs on the other hand are coated with a dye material that changes its reflective qualities when it is "burned" by a write laser, which is stronger and a different frequency than the read laser. How well a given optical drive can read one of these burned lasers is a function of many things including:

    • In the drive that burns an optical disc
      • The quality of the refelctive layer of the media
      • The specific dyes used for the particular brand and model of the media
      • The exact frequency and strength of the "write" laser
    • In the drive that is reading the disc
      • The exact frequency of the "read" laser in the drive
      • The sensitivity of the read diode in the drive
      • Any dust or dirt that may obscure the signal in the drive

    At one time it was estimated that more than 20% of burned optical discs could be read in any given drive. This has improved over time but it is still true that not all discs can successfully be read in all drives. It is also true that optical drives are notoriously short lived. It is also relatively common that one function, say reading DVD-RW drives whille others such as CD-Rs will still work.


    About the only thing you can change that effects what discs a given drive will read (or write) for that matter is dust and other detritous in the drive. Almost any office supply store will sell you a CD/DVD drive cleaning disc. They are not the easiest thing to use in slot loading drives but it can be done and may improve the number of discs your drive may read.


    If the discs you are having problems reading are the mechanically stamped commercial discs, you need a new optical drive. If your mini is under warranty or AppleCare take it to the Genius Desk.

  • Ardwa Level 1 (0 points)

    Ye Gods!


    Joe, either you got a lot going on in your head, are really hooked on being helpful or need a holiday ;-)


    Seriously folks - Thank you very much for a complete, concise and erudite answer to my poor question. Brilliant!


    Unless it was copied and pasted - hee hee!


    A seriously successful answer; well written and a joy to read.


    Such a shame most silly questions are not treated with the same care as you obviously have here.


    Congratulations and again "Many Thanks"