The growing power and number of high performance computing resources made available through computational grids present major opportunities as well as a number of challenges. At issue is how these resources can be accessed and how their power effectively exploited. We introduce the concept of grid application virtualization to address grid-based HPC usability. We then describe a middleware tool that we have developed to realize the virtualization of grid applications, the Application Hosting Environment (AHE), and describe the features of our new release, AHE 2.0, which provides access to a common platform of federated computational grid resources in standard and non-standard ways.

We then describe computational science research that uses 'petascale' resources to achieve scientific results at unprecedented scales and resolution. The applications span a wide range of domains from investigation of fundamental problems in turbulence through nanomaterials science research to biomedical applications at the forefront of HIV/AIDS and cancer research as well as cerebrovascular haemodynamics. A significant part of this recent work was performed on TeraGrid’s ‘petascale’ resource, Ranger, at Texas Advanced Computing Centre. We have sought to optimally use this large computer across application domains and scales, exploiting the excellent parallel scaling performance found on up to at least 32 768 cores for certain of our codes in the so-called ‘capability computing’ category as well as highthroughput intermediate scale jobs for ensemble simulations in the 32–512 core range. We also report on the parallel performance of some of our codes on up to 65 636 cores on the IBM Blue Gene/P system at the Argonne Leadership Computing Facility. The talk will stress the importance of a balanced grid infrastructure, supporting not only such massive computing resources but the ability to move data across fast networks, in conjunction with smart middleware and policies which support advance reservations and urgent computing.