What is the difference?

I’ve been using Nero 7 for some years now as my DVD burning programme. I’ve always burned on DVD setting. But recently I’ve got to wondering what the difference is between the three options. The options are DVD, DVD-9 and DVD-1 (8cm) - so, what is the difference ?

DVD-9 would be for dual-layer DVD discs, i.e. those with 8.5GB capacity.
DVD-1 8cm would be for 8cm recordable DVDs, e.g. the small 1.4GB discs typically used in DVD camcorders.

Thanks for the info. Now I know. Cheers.