Desktop grids from volunteer distributed computing to high throughput computing production platforms

Desktop Grids, literally Grids made of Desktop Computers, are very popular in the context of "Volunteer Computing" for large scale "Distributed Computing" projects like SETI@home and Folding@home. They are very appealing, as "Internet Computing" platforms for scientific projects seeking a huge amount of computational resources for massive high throughput computing, like the EGEE project in Europe. Companies are also interested of using cheap computing solutions that does not add extra hardware and cost of ownership. A very recent argument for Desktop Grids is their ecological impact: by scavenging unused CPU cycles without increasing excessively the power consumption, they reduce the waste of electricity. This book chapter presents the background of Desktop Grid, their principles and essential mechanisms, the evolution of their architectures, their applications and the research tools associated with this technology.