The system of one or several quantum wells embedded in a planar semiconductor Fabry-Perot microcavity with distributed Bragg reflectors is studied in the framework of both a semiclassical and a full quantum theory. The results obtained with the two treatments are proved to be equivalent. Simple analytical expressions for the exciton-radiation mixed mode energies are obtained. In particular the model of two coupled harmonic oscillators for the dispersion is shown to hold in the whole range of coupling constant and mirror reflectivity values. The theory describes at the same time the weak coupling regime, where an enhanced spontaneous emission takes place, and the strong coupling regime where instead a Rabi splitting in the dispersion can be observed. Existing experimental results are described with great accuracy. Analytical expressions for the splittings in reflectivity, transmission absorption, and photoluminescence are given. The splittings are all different from each other, and the differences could be observed in structures with suitably chosen parameters.