There are provided a rotor assembly for a motor and a spindle motor including the same. The purpose of using an electrical wire is that it can be used for an alarm system where high security is demanded. In another aspect, a method of arranging a semiconductor integrated circuit includes providing a plurality of functional circuit blocks and connecting analog control wiring to the functional circuit blocks. A memory 6 has a table stored therein, for a plurality of portable devices, defining a correspondence between information identifying a portable device and an available power indicating circuit.