Lawrence Berkeley National Laboratory

Community Climate System Model (CCSM) is currently a multi-executable system based on the Multi-Program Multi-Data (MPMD) mechanism. Each component is compiled into a separate executable. MPMD is normally cumbersome in usage and vendor support is sometimes limited or completely unavailable, such as on BlueGene/L. Also smaller groups and institutions would like to run CCSM locally, rather than relying on large computer centers. So, single-executable CCSM is under request. We are developing a multi-executable and single-executable coexisting version of CCSM. In single-executable, each component is organized as a subroutine, which is called from a master program. Different components run simultaneously. This is accomplished by redesigning the top level CCSM structures using the Multi-Program Handshaking (MPH) library.