1 Introduction
Today, the performance improvement and cost reduction of personal computers are remarkable. Many companies and education facilities have been introducing a lot of PCs as powerful and economical computational resources. However, most of them are used only for lightweight tasks such as documentation, e-mail, Web browsing, and so on. Furthermore, they are not used during nights and holidays. Thus, it can be considered that they have a large amount of unused computational power, and the total of them becomes enormous. Grid [1] and some other coarse-grain distributed computing are ideas to utilize surplus computational power. SETI@home [2] is one of the well-known succeeding applications of the coarse-grain distributed computing.