Difference between DVD and Blu-ray?

[Tom_Ryan]

Originally Posted by andy

I wonder why no one has ever applied that coating to DVDs or CDs? I see no reason that it couldn't be used on any optical disc, and maybe even other things like sunglasses.

$ + let DVD's wear out faster

[Jeffhs]

Originally Posted by Tom_Ryan

$ + let DVD's wear out faster

I cannot see how DVDs (or audio/data CDs, for that matter) can wear out. They are read by lasers, as opposed to video cassette and video/audio tape recorders that use heads which can gouge the surface of the tape as they wear; also, oxide can wear off any audio or video tape after years of use, although I have seen and heard some 30+-year-old audio tapes that still sound as good as the day they were made (I have audio cassettes that may be 15 years old and sound great). I have videocassettes I recorded 20 years ago (plus a few professionally recorded ones), as well, that still play every bit as well as when they were first recorded.

I think most audio and video cassettes fail because of mechanical trouble with the player in which they are listened to or viewed, not in normal use in a properly-operating player. I lost an audio cassette with irreplaceable music on it about a year ago, when my stereo cassette deck jammed and pulled the tape out of the cartridge (!). I've lost videocassettes the same way over the years. I remember one instance a few years ago, in which I had just taped a movie on one of the cable channels; my VCR jammed or developed some problem that wound the tape around the head drum and who knows where else. I practically had to wreck the VCR to get the cassette out. Worse, I never got to see the movie I had taped.


Phonograph records are read (for want of a better word) by ceramic or magnetic cartridges to which small needles (styli) are attached; of course, these styli do wear out after so many hours of use. Phonograph records can last years or decades under normal use; however, if the stylus is so badly worn that its tip is more akin to a chisel than to a phono stylus (as it would be after many years of use), it can gouge the grooves and damage or destroy the record in no time flat. This is why many audio enthusiasts, myself included, transfer their phonograph records to tape and later CD, keeping the original record for a backup.

Unless CDs and/or DVDs get scratched deeply or otherwise damaged severely (say by, heaven forbid, grinding the disc, data side down, underfoot on a concrete sidewalk[!] as some kids will do with discs they either don't like or in a fit of anger), these optical discs should last quite a while. The setup and recovery CD for my computer, for example, is nine years old, and still works as well as the day I bought the computer; the setup discs for my broadband Internet service are several years old as well and are still readable and usable, as are all of my data storage discs and music CDs. However, I did have one data disc come up as unusable (my computer's CD drive reported that the disc was severely damaged and could not be formatted, let alone used for data storage) several days ago while I was trying to back up files on the computer.

CDs are already coated in most cases (except, perhaps, for cheap off-brand discs), so small scratches should not ordinarily affect their operation. Data, CD and DVD playback devices, moreover, have error correction systems that will make several attempts to read a disc, before declaring that disc unusable. This means that a CD with visible scratches, if they aren't too deep or too long, will probably work as well, for years, as they are meant to in your computer, audio CD player or DVD player.

However, no error correction system, no matter how well it does its job, can work miracles. As I said above, very severe scratches on CDs or DVDs can and in almost all cases will render the disc unusable for anything other than a coaster or a miniature Frisbee.