The invention is a hard-disk-drive (HDD) assembly that includes a flame having the exterior dimensions of a particular form-factor HDD, an HDD with a form-factor smaller than the frame, a pair of mount assemblies that support the HDD entirely within the larger form-factor frame, and an electrical cable located entirely within the frame and having one end connected to the HDD and the other end exposed to the frame exterior at the position determined by the specifications of the larger form-factor. The HDD assembly thus presents a smaller form-factor HDD as a fully plug-compatible alternative to a larger form-factor HDD. The mount assemblies have spring-like cantilever arms in contact with damping material to provide a highly-damped nonlinear spring system that provides mechanical-shock resistance for the HDD in a direction normal to the planes of the disks and high stiffness in a direction parallel to the planes of the disks.