A computer system including a number of option bays that accommodate optional peripheral equipment, such as CD-ROM drives, DVD drives, magnetic tape backup systems and Zip drives. An unpopulated bay is segmented into compartments by a divider that extends through substantially the entire depth of the bay so that each of the compartments operates as a waveguide beyond frequency cutoff (WBFC). The resulting compartments are characterized by cross-sectional dimensions that are less than the cross-sectional dimensions of the bay, so that the compartmentalization effects substantially enhanced attenuation of electromagnetic signals having a frequency at the highest expected operating frequency of the computer system.