system 10 while the system is under its operation so called u201c hot plug u201d 0041 fig2 is a diagram to illustrate an inner register configuration of a control register 131 included in one embodiment of the present invention the control register 131 includes a main memory space resource range register 21 and an io space resource range register 22 the main memory space range register 21 designates a range of main memory space main memory space resource range to be controlled by the pci bus bridge 13 with its start address and end address the io space resource range register 22 designates a range of io space io space resource range to be controlled by the pci bus bridge 13 0043 fig3 is a diagram to illustrate one example of screen set up screen displayed on the operating terminal 16 for setting of reserved resources by user i e resource for hot plug at set up process a value that the system holds present current value and value when the system will hold at next start next value of the resource for main memory space mem resource and the resource for io space io resource at hot plug process are displayed the user beforehand researches a required resource for pci device which has a possibility to be utilized in the future and set up the reserved resource to be allocated to the vacant slot 19 at this screen the computer system 10 sets up on the pci bus bridge 13 resources to be allocated to the respective pci devices 151 152 15 n and reserved resource which is capable of being allocated to the vacant slot 19 on the basis.