Scratched CD

[simsfreq]

This morning I picked up a CD of mine to find a scratch going straight across it. I played through it and the whole CD played without a hitch!

Impressive... I thought so anyway. So how come it didn't affect it?

[henneth]

When CD's first came out, it was said they were resistant to alot of damage. In fact you could even eat your dinner off them. As a result I've replaced most of my crockery with cheap CD's from the bargain bucket at Woolworths. Although they don't hold alot, they are perfect for beefburgers or individual savoury pies, just don't put them together in the microwave.

[DiscoStu]

Yeah, Henneth, and they also make fabulous bagel props!

[delboy3]

The laser doesn't touch the disc so any (minor) scratches won't affect it. But beware of big specks of dirt or greasy fingerprints...

[pixellent]

The real answer to this is really quite complicated - so if you fancy a geeky 5 minutes read on.......
Cds store digital data (music in this case) as a series of little bumps on a spiral groove stamped into a very thin sheet of aluminium foil sandwiched between two shhets of plastic. This is by no means perfect, if you look at a cd against a bright light you can actually see through it and you can also see hundreds of tiny holes and imperfections.

So the data is actually repeated many times but in a such a way that you can lose large chunks of it, but by a mathematical process it can nearly all be recovered perfectly.

This process is called 'reed-solomon crossed interleaved error correction" and was developed in the 1960s as a means of retreiving the data from the very weak signals sent from mars by the mariner space probes.

[sheffwed39]

it is also scientifically proven that any westlife cd's make perfect tea coasters.