The present study investigates heat transfer and flow characteristics inside co-rotating disks simulated on the 3.5″ Hard Disk Drives (HDD). The experiments are conducted for the various operating conditions, such as hub height, rotating Reynolds number and head-arm length. A naphthalene sublimation technique is used to determine the detailed local heat transfer coefficients on the rotating disks. Numerical calculations are performed simultaneously to investigate the flow patterns induced by disk rotation. The results show that the heat transfer on the rotating disk is enhanced according to the increase of the rotating Reynolds number. The head arm inserted in the cavity between the rotating disk and the cover enhances uniformity of the heat/mass transfer on the disk due to the deficit of the momentum.