Experiments were performed to map local heat transfer coefficients on an unobstructed co-rotating disk system simulating the internal component of a computer disk drive assembly. The disk diameter was twice as large as a hard drive, and the rotational speed up to 5000 rpm was studied. The effects of two parameters, on the heat transfer phenomena the Reynolds number from 6.587 x 10(4) to 3.096 x 10(5) and the non-dimensional disk-to-disk ratio (L/D ) from 0.02 to 0.06, were observed. The disks were positioned horizontally, and heat transfer was measured for the top faces of both disks. Emphasis is given to the top face of the lower disk in this research, as less experimental data are available in the literature. A transient liquid crystal technique was employed for the measurements, and the results reveal an interesting pattern of the heat transfer rate in the gap for the upper surface of the lower disk. The overall heat transfer is much lower for the surface of the lower disk as compared to that of the top disk. The maximum average heat transfer rate was established to be at L/D = 0.04 for the case with the highest rotational speed.