is connected to the portable computer 100 via a bus and a default data transmission port and there is an smi system management interrupt signal line and a polling signal line extended between and connected to the keyboard controller 13 and the system bios 12 the keyboard controller 13 may send an smi signal smi to the system bios 12 via the smi signal line and the system bios 12 may send a polling signal s 1 via the polling signal line for polling about a state signal of a default signal port 131 of the keyboard controller 13 in the default signal port 131 there is included at least a default status bit standing for a state that an interrupt signal has been sent out by a falling sensor in a typical notebook computer currently available in the market the default signal port 131 of the keyboard controller 13 may be signal port 6 c for example and the default status bit in the signal port 6 c is bit 7 the hard disk 14 is connected to the portable computer 100 via a bus such as an ide interface bus and a default data transmission port and the system bios 12 may send a parking control signal s 2 to the hard disk 14 via a signal line so as to drive the hard disk 14 to park or to un park a falling sensor 2 is connected to the keyboard controller 13 via a signal line when the falling sensor 2 senses a falling state of the portable computer 100 that is when the falling sensor 2 detects an acceleration signal that exceeds a preset acceleration signal level an interrupt signal int is triggered by the falling sensor 2 to the keyboard controller 13.