A computer system with a main memory is equipped with an HDD that has a disk and a driving motor driving the disk, a non-volatile storage unit provided in the HDD storing therein a booting program of an operating system, and a control unit reading out the booting program stored in the non-volatile storage unit and loading the booting program onto the main memory before the driving motor reaches a normal speed as power is supplied to the computer system. With this configuration, there is provided a computer system capable of reducing the booting time of the HDD.