We have performed parallel self-consistent field (SCF) calculations in continuum to study the self-assembled morphology of symmetric diblock copolymers in nanopores. The SCF equations are solved with high accuracy in real space, without a priori knowledge of the possible morphologies. The surface preference and pore diameter are varied systematically, and various morphologies are found as stable phases. Our calculations reveal the formation mechanisms of these morphologies, which can be understood from their counterparts in thin films confined between two homogeneous surfaces with different preference. We have also compared our SCF calculations with available experiments, Monte Carlo simulations, and a strong-stretching theory.