optical storage - discs

[Turbonium]

A couple questions I've never wrapped my head around:

1. If optical storage is based on a very thin, sensitive-to-the-micrometer layer of chemical "stuff" with precise "pits" in it, when I bend the CD/DVD back and forth, how come the data stays intact? You would think it damages the chemical layer and the "pits" it contains...

2. Whenever a CD/DVD is burned, errors always happen, correct? Then how come optical storage is still considered a reliable method of data backup and storage? And also, why is the databurned considered to be an "exact copy" if it's burned with some errors on it?

I have no clue of the answer to 1., and for 2., my only guess is that the errors are detected during burning, and are simply re-burned immediately during the process (with the total number of errors being so small that it makes no impact on the total size needed on disc to complete the burn).

 

[The Boston Dangler]

1. Don't bend it. There is some flexibility, but many DVD cases need too much force to remove the discs. It's more likely you'll crack the plastic before you damage the data.

2. http://www.cdfreaks.com/

 

[Turbonium]

I never said I bend discs on purpose, but it's just a thought. Based on my explanation, you'd think bending it even slightly would damage the data.

I know for a fact that you can bend them to extremes and the data is still 100% intact. I've tried it with useless CDs.

 

[Mday]

1. there is some flex. the extreme bending you mention may not show signs of damage now, but it has reduced the useful life of the disc

2. CRC.

 

[CycloWizard]

#1 has to do with the material properties of the CD/DVD. Without going into too much detail (though I can if you're really that interested), as long as the disc is in the elastic region, no permanent deformation occurs: once the load is released, it regains its original form. The amount of deformation that the disc can take before it leaves the 'elastic region' and begins plastic (permanent) deformation depends on the material components that make it up. The amount of force it takes to leave the elastic region depends on the modulus of the material.

So basically, it's because the plastic (and whatever else is used in the discs) is specifically chosen to allow some bending without deforming in a non-reversible manner.