  We revisit the linear MRI in a cylindrical model of an accretion disk and
uncover a number of attractive results overlooked in previous treatments. In
particular, we elucidate the connection between local axisymmetric modes and
global modes, and show that a local channel flow corresponds to the evanescent
part of a global mode. In addition, we find that the global problem reproduces
the local dispersion relation without approximation, a result that helps
explain the success the local analysis enjoys in predicting global growth
rates. MRI channel flows are nonlinear solutions to the governing equations in
the local shearing box. However, only a small subset of MRI modes share the
same property in global disk models, providing further evidence that the
prominence of channels in local boxes is artificial. Finally, we verify our
results via direct numerical simulations with the Godunov code RAMSES.
