We applied the virtualization technology to the server computers to form a high-available redundant server system. At the same time, we replaced general purpose PC computers by thin client terminals. The introduction of these technologies reduced the number of computers substantially and gave an opportunity for us to achieve the high-available computing systems with less management cost. To ensure high-availability, the server computer has to be built by using reliable components with redundant architecture instead of reducing the number. The application processing performance of the client OS on the host OS was greater than or equal to that of measured by a stand-alone server. The combination of the recent multi-core architecture server and Xen OS showed good performance as a result of appropriately allocating system resources to Xen OS. The thin client system is useful to integrate widely scattered terminals in the site to small number of systems, which ease maintenance effort a lot. The integrated virtual-machine system and thin client system use a network attached storage (NAS) system that runs under the redundant configuration.