We propose a new approach for developing parallel I/O- and compute-intensive applications. At a high level of abstraction, a macro data flow description describes how processing and disk access operations are combined. This high-level description (CAP) is precompiled into compilable and executable C++ source language. Parallel file system components specified by CAP are offered as reusable CAP operations. Low-level parallel file system components can, thanks to the CAP formalism, be combined with processing operations in order to yield efficient pipelined parallel I/O and compute intensive programs. The underlying parallel system is based on commodity components (PentiumPro processors, Fast Ethernet) and runs on top of WindowsNT. The CAP-based parallel program development approach is applied to the development of an I/O and processing intensive tomographic 3D image visualization application. Configurations range from a single PentiumPro I-disk system to a four PentiumPro 27-disk system. We show that performances scale well when increasing the number of processors and disks. With the largest configuration, the system is able to extract in parallel and project into the display space between three and four 512×512 images per second. The images may have any orientation and are extracted from a 100 MByte 3D tomographic image striped over the available set of disks