Unified Parallel C (UPC) is an extension of the C programming language designed for high performance computing on large-scale parallel machines. The language provides a uniform programming model for both shared and distributed memory hardware. The programmer is presented with a single shared, partitioned address space, where variables may be directly read and written by any processor, but each variable is physically associated with a single processor. UPC uses a Single Program Multiple Data (SPMD) model of computation in which the amount of parallelism is fixed at program startup time, typically with a single thread of execution per processor. Berkeley UPC provides a portable, high-performance compiler for developing UPC software on systems ranging from clusters to custom supercomputers and even laptop-grade systems.
GASNet (Global-Address Space Networking) is a language-independent low-level networking layer that provides network-independent, high-performance communication primitives tailored for implementing parallel global-address space SPMD languages such as UPC, Titanium, and Co-Array Fortran. The interface is primarily intended as a compilation target and for use by runtime library writers (as opposed to end users), and the primary goals are high performance, interface portability, and expressiveness.