A disk drive within the dimensional confines of a form factor can optimise volumetric density by using the full height dimension to house disks (13), but must thereafter utilise the remaining space for electrical components. The structure shown uses a stack of parallel cards with an interface card (84) on the rear end wall to provide the principal drive control and data circuits outside the head-disk assembly (HDA; 13). The motor driver circuitry (107, 111) is mounted on a flat flexible cable (72) and is secured to the front wall (18) at the opposite end of the drive in heat transfer relation. The heat generating motor drive circuits are physically isolated from the data/control circuits by the frame and HDA while some of the printed circuit cards are secured to the frame in a manner that enhances rigidity; the allocation of modules to the cards anticipates flow of data and control signals so as to minimise the number of connections and signal delays that impair performance.