What is the difference between self inking rubber stamps and pre inked rubber stamps?

Rubber Stamps Of The Pre Inked Variety

To put it simply, the self inking rubber stamp has an inner mechanism that flips the die and actually stamps it on an inner stamp pad before transferring the text and or art message to a piece of paper.  In a pre-inked stamp, there are no moving parts, no mechanical motion that impacts the die into an inner pad.  Pre-inked stamps simply have a different type of die which actually acepts ink, and these dies are then pre-inked in a prescribed manner, so the image from the die can be transfered to the paper simply by pressing the stamp onto the paper.

Xstamper makes the best pre inked stamps in the world, while good self-inkers are made by a number of companies including Ideal and Trodat.