Patent ID: 8010719

Claim:
A virtual machine system disposed on one computer device including a CPU, a memory, and an IO interface, the virtual machine system comprising: a hypervisor that generates plural virtual servers, each of the virtual servers individually executing an operating system; and an IO controller that controls the IO interface, the IO controller being located between the IO interface and at least one of the CPU and the memory, and wherein the IO controller has: a DMA receiving unit that receives DMA requests from the IO interface; a virtual server locating unit that identifies the virtual servers corresponding to the received DMA requests; a DMA monitoring counter that monitors DMA processing status for each of the virtual servers; a threshold register set in advance for each of the virtual servers; and a priority deciding unit that compares the DMA monitoring counter and a value of the threshold register, the priority deciding unit deciding the priority of processing of the received DMA requests; wherein: the DMA monitoring counter holds credit information indicating the number of receivable DMA requests; the priority deciding unit assigns high priority to the received DMA requests when the credit information exceeds the threshold register value; and the priority deciding unit assigns low priority to the received DMA requests when the credit information-is less than the threshold register value.