Thanks a lot. Before I thought wiki stores only diff's between versions. As we can think that the most simple compression method is saving the diff sections For example, in order to save 
{1000, 1003, 1005, 1021, 1240, 1241} we only needed to save {1000, 3+, 2+, 16+, 1240, 1+}, and
this is indentical to the basic of image compression like jpeg, or motion compression like mpeg.
In order to save motion pictures, mpeg used I frame, P frame, P frame, ..., I frame, P frame, ....,
so I was suprised to hear that wiki saves all the verion in full text format. Anyway thanks. 
It would be great to have a page something like wikipedia:wikipage storage format that explains
in detail how the wikipedia saves its every pages of every version in detail and how the editing warrings (edit battle?) effects on the storage usage and how a single character addition effects on the storage usage, etc. If you had some authority on wiki and knew the stroge mechanism of wiki, how about to edit that page? Just a thought. Anyway thanks. (  )