Scientific computing using virtual high-performance computing

High-performance computing systems are important in scientific computing. Clusters of computer systems --- which range greatly in size --- are a common architecture for high-performance computing. Small, dedicated clusters are affordable and cost-effective, but may not be powerful enough for real applications. Larger dedicated systems are expensive in absolute terms and may be inefficient because many individual groups may not be able to provide sustained workload for the cluster. Shared systems are cost-effective, but then availability and access become a problem.