Computer science core instruction attempts to provide a detailed understanding of dynamic processes such as the working of an algorithm or the flow of information between computing entities. Such dynamic processes are not well explained by static media such as text and images, and are difficult to convey in lecture. The authors survey the history of visualization in computer science education, focusing on artifacts that have a documented positive educational assessment. Changes in how computing technology has affected the development and uptake of such visualization artifacts in computer science education, and how recent technology changes are leading to progress in developing online hypertextbooks are then discussed.