VIRTUAL COMPUTER SYSTEM

PURPOSE:To determine the specification of a virtual computer identifier independently of the capacity of an I/O device by arranging plural identifiers and a registration table for the upper and lower addresses of storage areas corresponding to the identifiers in the I/O device. CONSTITUTION:An instruction 400 is inputted to an instruction execution control part 150, decoded by an instruction code and interpreted as a virtual computer identifier (VMID) registering instruction. An instruction execution part 150 sends the specified VMID, the contents of a general register and the upper and lower limit addresses to an upper/lower limit entry control part 420 in the I/O device. If an entry has a blank, the control part 430 registers the transmitted VMID and the upper and lower limit addresses alpha, beta in a registration table 440. In this case, a hardware corresponding to the VMID determines the VMID (HVMID) to be discriminated and registers the determined VMID in the same entry.