The invention discloses a computing system such as a computer, a Personal Digital Assistant, or a mobile phone, being connected both to an internal network and an external network and being able to quickly and safely switch therebetween without being shut down while ensuring a physical separation between the two networks. When a user inputs a request of switching, a switching unit will set a trigger thereof and generate a consequent non-maskable interrupt to CPU. After receives the NMI, the CPU controls the switching unit to run a switch program kept therein to back up a current status of the system. Then the switch program backs up a current status, controls the switching unit to interrupt all serving programs and loads the other status other than the current status to the computing system, and finally control the switching unit to reset the trigger.