  We propose a simple string bit formalism for interacting strings in a plane
wave background, in terms of supersymmetric quantum mechanics with a symmetric
product target-space. We construct the light-cone supersymmetry generators and
Hamiltonian at finite string coupling. We find a precise match between string
amplitudes and the non-planar corrections to the correlation functions of BMN
operators computed from gauge theory, and conjecture that this correspondence
extends to all orders in perturbation theory. We also give a simple RG
explanation for why the effective string coupling is g_2 = J^2/N instead of g_s
= g_{ym}^2.
