CD / DVD Compatibilty with Drives

  PaulB2005 16:28 30 Nov 05

Following on from click here

Why are some media compatible and others aren't with some drives?

Also do CDs and DVDs go "off"? Even when kept in cool dark place?

Any reason why Sony CDR should suddenly stop working with a drive after 60+ successfull burns?

  Shortstop 16:36 30 Nov 05

I read your postings with interest, but didn't post because I could not offer a solution. About 18 months ago a similar string was started and I remember that someone posted a link where you could buy 50 CDs in a single pack - but by various makers - so that you could see what works and what doesn't in your CD writer. I bought these and realised that there was little difference between very expenive and 'normally' priced CDs but those at the cheap & cheerful end wouldn't work for me. Having said that, my daughter bought the same pack but now only uses the cost effective CD-Rs. She only rarely burns a coaster, so I guess that it's horses for courses.

One last thing though, I wish I could remember where I bought the CDs from [I've changed my forum name & cannot access my previous postings] as I am wondering if the same kind of thing is available for DVDs



  Fruit Bat /\0/\ 19:10 30 Nov 05

To put the required CD player servo system performance into perspective, here is an analogy:

At a constant linear velocity of about 1.2 meters per second, the required tracking precision is astounding: Proper tracking of a CD is equivalent to driving down a 10 foot wide highway (assuming an acceptable tracking error of less than +/- 0.35 um) more than 3,200 miles for one second of play or over 14,400,000 miles for the entire disc without accidentally crossing lanes! Actually, it is worse than this: focus must be maintained all this time to better than 1 um as well (say, +/- 0.5 um). So, it is more like piloting a aircraft down a 10 foot wide flight path at an altitude of about 12 miles (4 mm typical focal length objective lens) with an altitude error of less than +/- 7 feet! All this while the target track below you is moving both horizontally (CD and spindle runout of 0.35 mm) 1 mile and vertically (disc warp and spindle wobble of up to 1 mm) 3 miles per revolution! In addition, you are trying to ignore various types of garbage (smudges, fingerprints, fibers, dust, etc.) below you which on this scale have mountain sized dimensions. Sorry for the mixed units. My apologies to the rest of the world where the proper units are used for everything).

The required precision is unbelievable but true using mass produced technology that dates to the late 1970s. And, consider that a properly functioning CD player is remarkably immune to small bumps and vibration - more so than an old style turntable. All based on the reflection of a fraction of a mW of invisible laser light!

Of course, this is just another day in the entertainment center for the CD player's servo systems. Better hope that our technological skills are never lost - a phonograph record can be played using the thorn from a rosebush using a potter's wheel for a turntable. Just a bit more technology is needed to read and interpret the contents of a CD!

And, for a DVD with its narrower longer track (0.74 um compared to 1.6 um and more than twice as long), it's even more of a challenge!

  PaulB2005 07:25 01 Dec 05

I see..........


  SG Atlantis 07:47 01 Dec 05

Just so I can read Fruit Bat's response another five or twenty times.


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