Abstract: Digital computer clock and data transfer rates are increasing at an astonishing rate. Clocks are available that operate at 1GHz (1 billion changes per second). The clock and data pulses are in the form of trapezoidal pulses with ever-smaller rise and fall times. Typical rise and fall times are on the order of 50ps. The spectral content of these clock pulses consists of harmonics at the basic repetition rate (1GHz, 2GHz, 3GHz,…..). The levels of these components are determined to a large degree by the rise/fall time of the pulses. Hence today’s clock pulses have a very wide spectral content well into the middle GHz range. In order for digital computers to function properly, the propagation delay of the interconnecting lines must be within certain bounds. Line lengths of several centimeters were inconsequential in this regard for "older" computers whose clock speeds were 100MHz and rise/fall times on the order of nanoseconds. This talk will focus of the numerical modeling of those interconnect lines using the Finite Difference Time Domain (FDTD) method. High-frequency skin effect loss on those lines is becoming an increasing concern with regard to the degradation of the pulse shapes and levels. The FDTD method provides an effective method to incorporate those frequency-dependent skin effect losses.