for each power management timer has elapsed since a last user access an interrupt is generated across the bus 12 almost all the pcs that are currently sold have the hardware components equivalent of the blocks 11 through 32 although many other hardware components are needed to constitute a pc this is obvious to one having ordinary skill in the art and to simplify the description no explanation for them will be given in this specification in this embodiment the functions of the lcd off timer the suspend timer and the hibernation timer are provided by the power management processor 45 and the functions of the hdd off timer is provided within the hdd 22 such an arrangement in which hardware blocks these power management timers are located is merely a matter of design fig2 is a specific diagram showing a power supply system for the pc 100 according to the embodiment of the present invention the dc dc converter 43 which is shown as a single block 43 in fig1 is actually constituted by two blocks a dc dc converter 43 1 for supplying a voltage of 5 v and a dc dc converter 43 2 for supplying a voltage of 3 3 v in correspondence with the dc dc converters 43 1 and 43 2 the fet switch 44 in fig1.