Description New 3D server architecture for better energy-efficient Data CentresData Centres (DCs) are a key resource for innovation and leadership of industry in Europe. They drive the Information Society through hosted cloud applications. To sustain the ever-increasing demand of storing and processing data, DCs need to improve their capabilities and scale in size. With current server technology, however, DC scaling is limited by the IT equipment’s density and energy consumption. To keep up with data growth, the IT equipment must become dramatically smaller and more efficient in power and energy. This moves the focus of server design from performance to power/energy efficiency and total cost of ownership (TCO). The basic components of future servers and their integration into a full system must be reconsidered from the ground up. The processor, the memory hierarchy, I/O, the system interconnects and the software all require fundamental changes to match the applicationperformance requirements in less space and with drastically lower energy costs. EUROSERVER is addressing these challenges in a holistic manner; we advocate the use of state-of-the-art lowpower ARM processors in a new server system-architecture that uses 3D integration to scale with the numbers of cores, and the memory and I/O, all managed by new systems software providing transparent system-wide virtualization and efficient resource use by cloud applications. The EUROSERVER prototype will demonstrate how the proposed approach can lead to 10x DC Energy Efficiency by 2020.