h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Although CD's remain single sided, there was some talk a few years ago of developing CD's with 2 recordable layers, one on top of the other. The laser could be focused on one layer, while passing straight through the other, or not reaching it at all (depending on which layer was being read). However, I haven't heard of any developments on this front. People just moved on to DVD's, which have a greater storage capacity.

Cheers Justin I'm currently reworking this for re-submission, so will include this bit of info in the new improved article.

Funny you should mention that, because DVDs come in both dual-layer and double-sided flavours. I don't suppose they'll ever get round to applying the technology to CDs now though.

Wouldn't you have to turn a double sided DVD over? Plus it means both surfaces need to be kept undamaged.

Just remembered a couple of things I heard on a radio programme a week or two ago (can't remember exactly when/what it was).

1) The recording length was set at 74 mins so that the inventor (I think) would be able to listen to his favourite piece of classical music (again, can't remember what it is) without having to get up and change the disc.

2) CD's don't actually give a 'real' souond. The highest frequencies (ie pitches) get 'chopped off' during the recording process. I'm not sure, but I think it's to increase the available playing time (to get it to that 74 minute mark).

You've just spotted both the problems with double sided DVDs! The only one I've come across so far is the South Park movie, which has the widescreen version on one side and the normal version on the other.

Oh, and all the label information has to be on a tiny little band around the centre hole, because obviously they can't print on either side of the disc.

I think the piece of music was Beethoven's 5th.

Been meaning to add this for a while - apparently someone's come up with an eight-layered CD - each layer is a different transparency (I think) so can be read independantly. Be interesting to see if anything comes of it.

Wow!!! ant details Justin.

I do need to update this and get it approved don't I?

That was I want details.

D'oh.

I'll try and find some details for you DD.

Cheers Justin.