Disney Animation- How is it done?

Watch this video! Its amazing and really interesting!

I have always wondered just how Disney made the animations back in the early 1900's. Today we can just use Photoshop or something similar to make a little animated sequence in no time as broadcast it to the world on the internet. More and more animated films are being 'chucked' out as if they grow on trees and its remarkable that Disney were doing this, but so long ago, and without the technology we have these days.
I never knew how they actually got the individual frames to move with each other, but it seems on this video that they take stills of each frame then run it through a camera. Much like the process were are doing.
Its to see how they layered up the frames, using a painted background and layering the characters over the top [who were traced and painted by 100's of pretty ladies of course] to create a complete scene. Its really cool and shows just how much work went into the films!

This has given me a great little insight and the processes and ideas will come in handy for sure!