In order to take advantage of the significant benefits afforded by computational electromagnetic techniques, such as the finite-difference time-domain (FDTD) method, solvers capable of analyzing realistic problems in a reasonable time frame are required. Although software-based solvers are frequently used, they are often too slow to be of practical use. To speed up computations, hardware-based implementations of the FDTD method have recently been proposed. Although these designs are functionally correct, to date, they have not provided a practical and scalable solution. To this end, we have developed an architecture that not only overcomes the limitations of previous accelerators, but also represents the first three-dimensional FDTD accelerator implemented in physical hardware. We present a high-level view of the system architecture and describe the basic functionality of each module involved in the computational flow. We then present our implementation results and compare them with current PC-based FDTD solutions. These results indicate that hardware solutions will, in the near future, surpass existing PC throughputs, and will ultimately rival the performance of PC clusters.