Abstract: A shield against electromagnetic radiation emanating from a server includes a shielding apparatus attached to a server chassis which contains a set of hard disk drive modules. Each hard disk drive module includes a bracket and a hard disk drive fixed therein. A gap is defined between one end of each bracket and the hard disk drive held in the bracket. The gaps of the brackets extend from top to bottom. The top plate of the chassis defines a slot corresponding to the gaps. The shielding apparatus includes a mounting plate and a set of spaced shielding units set vertically to the mounting plate. Each shielding unit defines a set of electrically-conductive vents functioning as waveguides to absorb electromagnetic radiation.