Patent ID: 7890669

Claim:
A computer system, comprising: at least one node composed of at least one processor and memory; an I/O hub connecting at least one I/O card; a switch connecting the node and the I/O hub, and a plurality of logical servers, each being provided with an operating system and run by one or a plurality of the at least one node, wherein each of the logical servers is set in advance to allow one of exclusive use and shared use of the I/O card connected to the I/O hub via the switch, wherein the I/O hub allocates a virtual MM I/O address unique to each logical server to a physical MM I/O address associated with each I/O card, wherein the I/O hub keeps allocation information indicating relation between the allocated virtual MM I/O address, the physical MM I/O address, and a server identifier unique to a logical server corresponding to the allocated virtual MM I/O address, and wherein, when an access request designating the allocated virtual MM I/O address as an access destination is received, the I/O hub refers to the allocation information to extract, from the designated virtual MM I/O address, a corresponding physical MM I/O address to specify the I/O card as an actual access destination of the access request, and to extract the server identifier from the designated virtual MM I/O address; and, based on the extracted server identifier, identifies the a logical server that has issued the access request.