  We study a class of generalized models of gauge mediated supersymmetry
breaking (GMSB). We find the parameters and the full particle spectrum of the
minimal supersymmetric standard model (MSSM) for all GMSB models with messenger
multiplicities that satisfy the perturbativity of the gauge couplings up to the
GUT scale. We give a detailed description of the algorithm that has been used
to predict all the unmeasured parameters of the MSSM by taking (one-loop)
radiative effects into account. We also calculate the branching ratio $BR(b \to
s \gamma)$ and find that it always turns out to be larger than the standard
model prediction. However, we find that the branching ratio typically remains
within the current experimental bounds, except for some special cases with a
light charged Higgs boson, or a small supersymmetry breaking scale and a
negative $\mu$-parameter.
