Comparisons of the IMO and IOI

There are several International olympiads for secondary school students, but the five which are most widely recognised are those in mathematics, physics, chemistry, biology and informatics, in approximate order of founding. Most of these were originally founded under the auspices of UNESCO. Of these, the discipline most closely related to Informatics is mathematics, and in fact in several countries, for example Australia and Bulgaria (the latter of which can be credited as the founding country of IOI), the two olympiad programs are administered by the same organisation. The purpose of this paper is to compare the two olympiads in some detail, including tasks, topics, evaluation, etc. Despite the close relationship between the disciplines themselves, and the fact that there are similarities in the structure of the olympiads, in fact between all five, such as the medal structure, it is surprising also how different are the evolved traditions of IMO and IOI.