Grid architectures and the European DataGrid

The term "Grid" is used in reference with wide area (possibly planetary) computer networks that enable very large communities of users to access massive computational facilities, ideally with the same transparency and ease that users of electrical devices, whether industrial machines or home appliances, expect from the electrical power grid. This paper introduces the basic concepts of Grid architectures, drawing upon the experience of the European DataGrid project, one of the most important enterprises in this field, aimed at providing support to scientific communities involved in High Energy Physics, Earth Observation, and Biology.