How does DVD-RAM actually works?

Hello!

Well I actually understand how HDDs work, and I know RAM discs are similar. But I just can’t understand how a table recorder like my panny dmr-es10 can record and play a movie at the same time! Can the laser pickup move so fast (like a HD head) making it possible? Or are there 2 laser pickups inside my recorder (I don’t think is the case, since this would make the recorder project a lot more complicated)??

Thankyou very much!