A computer system accepting feature cards for, for example, coupling external peripheral devices includes a plurality of sockets mounted on the planar board to accept edge connectors on the cards, and slots in the main enclosure to permit coupling to external peripherals. To reduce electromagnetic radiation, the slots in the main enclosure have a depth such as to define channels, and the brackets on the cards are of U-shaped cross-section such as to fit within the channels. The channel walls are conductive, and the brackets are shaped to define spaced outward contact points which closely engage the channel walls.