In the last 50 years, the field of scientific computing has undergone rapid change --- we have experienced a remarkable turnover of technologies, architectures, vendors, and the usage of systems. Despite all these changes, the long-term evolution of performance seems to be steady and continuous.

The acceptance of parallel systems not only for engineering applications but also for new commercial applications, especially for database applications, emphasizes different criteria for market success such as stability of the system, continuity of the manufacturer and price/performance. Due to these factors and the consolidation in the number of vendors in the market, hierarchical systems built with components designed for the broader commercial market are currently replacing homogeneous systems at the very high end of performance. Clusters built with components off the shelf also gain more and more attention and today have a dominant position in the Top500.

In this talk we will look at some of the existing and planned high performance computer architectures and look at the interconnections schemes they are using.