This book describes the Splash 2 computing system as designed and built at the Supercomputing Research Center. This is a novel attached processor using Xilinx 4010 FPGAs as its processing elements and whose application programming language is VHDL. This is the first publication that details the complete Splash 2 project -- the hardware and software systems, the architecture and their implementations, and the design process by which the architecture evolved from an earlier version machine. This text allows you to understand why the machine has been engineered in the way it has. In addition to the description of the machine, several applications are described in detail, permitting the reader to gain an understanding of the capabilities and the limitations of this kind of computing device. The Splash 2 program is significant for two reasons. First, Splash 2 is part of a complete computer system that achieves supercomputer like performance on a number of different applications. The second significant aspect is that this large system is capable of performing real computations on real problems. In order to understand what happens when the application programmer is permitted to design the processor architecture of the machine that execute his programs, it is necessary to see the system as a whole. This book looks in-depth at one of the handful of data points in the design space of this new kind of machine.