  We propose a kinetic Ising model to study phase separation driven by surface
diffusion. This model is referred to as "Model S", and consists of the usual
Kawasaki spin-exchange kinetics ("Model B") in conjunction with a kinetic
constraint. We use novel multi-spin coding techniques to develop fast
algorithms for Monte Carlo simulations of Models B and S. We use these
algorithms to study the late stages of pattern dynamics in these systems.
