alt Hacker NewsDVD-RWs always seemed like complete magic to me. I had no idea how they worked, or why they worked. I made and wiped DVD-RWs as a teenager dozens of times, because my dad got annoyed that I kept using up all his DVD-R's, so I bought like three DVD-RWs and used them for all my experiments.
I don't think I got anywhere near the limits for any of them, as I don't remember getting any faults from them, but they were always cool to me.
I was also one of the happy few who had a DVD-RAM drive for my desktop as a teenager; I never really understood why DVD-RAM never caught on, because it seemed to work fine for me, and it was kind of nice not having to wipe the disk to erase stuff.
Well. There is a laser, the first time you write a DVD-RW the laser burns holes into the disc, those are your ones and zeroes. Then if you want to rewrite it you have to fill in the holes so the drive uses an epoxy covered brush to make sure the disc has a smooth layer, then it makes new holes.
It's really the one physically possible way to implement it if you think about it.