The National Center for Supercomputing Applications (NCSA) is the leading-edge site for the National Computational Science Alliance (Alliance), which is one of two recipients of the NSF's Partnerships for Advanced Computational Infrastructure (PACI) program. It anchors the partner teams and carries out much of the software development to support the Alliance. Led by NCSA at the University of Illinois at Urbana-Champaign (UIUC) with core funding from the NSF (upto $170M in the next 5 years) and the state of Illinois, the Alliance is building a National Technology Grid (Grid) which will integrate high-performance computers, advanced visualization environments, remote instruments, and massive databases via high-speed networks to form the most powerful problem-solving environment ever assembled. During the next decade, the Alliance aims at making the Grid as easy to use as the desktop is today. Researchers will work together and share ideas with ease through the use of collaboration technologies for the desktop or virtual reality. They will have at their disposal advanced searching and indexing capabilities, digital libraries, audio and video streaming, and virtual offices. It aims at creating a distributed computing grid populated with powerful computers that are individually scalable and that, when necessary, can be assembled into metacomputers. NCSA's focus is on the newly emerging distributed shared-memory (DSM) architecture. This platform combines the easy programmability of shared-memory symmetric multiprocessors (SMPs) with the scalability of the distributed-memory massively parallel processors (MPPs). NCSA already has a 512-processor SGI/CRAY Origin2000 which is supposed to be the largest unclassified CRAY Origin2000 in the world.