Flow inside a hard-disk drive (HDD) is investigated using a simplified 3.5″ HDD model with shroud opening and read-and-write arm (RWA). The model is designed to serve as a benchmark of HDD flow study both in experiments and in numerical simulations. The complex flow behavior in the narrow disk-to-disk space is focused with the RWA inserted into the space. The velocity statistics are acquired at totally 8 different locations using a velocity profile sensor with a spatial slot resolution of 30 μm along the axial direction. The measurement was carried out at the disk Reynolds number Red=2. 4×105 which corresponds to the rotation speed of 7700 rpm at a real 3.5″ HDD for desktop computers. The resulting mean velocities and Reynolds stress components are influenced by the shroud opening and especially by the RWA, compared to an axisymmetric model without an RWA. The highly sheared flow between the RWA and adjacent upper/lower disk was successfully captured in the experiment.