Dimer chains formed during deposition of Si on Si(100)-2X 1 at similar to 435 K have been analyzed using scanning tunneling microscopy. Results are compared with the outcome of Monte Carlo simulations. The size distributions obtained from experiments and the model give new insight into the basic mechanisms responsible for dimer chain formation. For the Monte Carlo simulations, activation energies for adatom diffusion of 0.7 and 0.5 eV, parallel and perpendicular to dimer row directions, gave the best agreement with experimental results.