We calculated an eddy current loss in a wire as a function of an applied ac field. Estimating the field at an actual coil wire and summing the losses in all points of wires we obtained a formula representing a coil loss. Based on the calculated results, we designed coils which drive thirty-two 64 kb chips. The observed loss of the coils was in good accord with the calculated one. This 2 Mb module was operated at 40 Oe rotation field of 500 kHz with the coil loss of 8 W.