for anybody who ever wondered...
... here's a fairly brief, tidy explanation of what a 12-inch LaserDisc actually contains, and how it works.
the gist of it is that, although a lot of LaserDisc content is created from a digital master copy (hence the reason that many early DVDs were mastered from the same source as previous LD versions... and you'll see the phrase "digitally mastered" on a lot of commercial VHS tapes too), the disc actually contains a form of analogue video that's read by a laser.
this knowledge doesn't seem to be very common at all, and it took me a while to dig it up. it's prolly the kind of trivia that will impress some of your more geeky, tech-oriented friends when you drop the science on them at parties.